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Monday, November 11, 2013
Monday, September 2, 2013
How Browsers Store Your Passwords
Introduction
In a previous post, I introduced a Twitter bot called dumpmon which monitors paste sites for account dumps, configuration files, and other information. Since then, I've been monitoring the information that is detected. While you can expect a follow-up post with more dumpmon-filled data soon, this post is about how browsers store passwords.
I mention dumpmon because I have started to run across quite a few pastes like this that appear to be credential logs from malware on infected computers. It got me thinking - I've always considered it best to not have browsers store passwords directly, but why? How easy can it be for malware to pull these passwords off of infected computers? Since sources are a bit tough to find in one place, I've decided to post the results here, as well as show some simple code to extract passwords from each browser's password manager.
The Browsers
For this post, I'll be analyzing the following browsers on a Windows 8 machine. Here's a table of contents for this post to help you skip to whatever browser you're interested in:
Chrome
Let's start with Chrome. Disappointingly, I found Chrome to be the easiest browser to extract passwords from. The encrypted passwords are stored in a sqlite database located at "%APPDATA%\..\Local\Google\Chrome\User Data\Default\Login Data". But how do they get there? And how is it encrypted? I got a majority of information about how passwords are stored in Chrome from this article written over 4 years ago. Since a bit has changed since then, I'll follow the same steps to show you how passwords are handled using snippets from the current Chromium source (or you justskip straight to the decryption).
Encryption and Storing Passwords
When you attempt to log into a website, Chrome first checks to see if it was a successful login:
We can see that if it's a successful login, and you used a new set of credentials that the browser didn't generate, Chrome will display a bar asking if you want your password to be remembered:
To save space, I'm omitting the code that creates the Save Password bar. However, if we click "Save password", the Accept function is called, which in turn calls the "Save" function of Chrome's password manager:
Easy enough. If it's a new login, we need to save it as such:
Again to save space, I've snipped a bit out of this (a check is performed to see if the credentials go to a Google website, etc.). After this function is called, a task is scheduled to perform the AddLoginImpl() function. This is to help keep the UI snappy:
This function attempts to call the AddLogin() function of the login database object, checking to see if it was successful. Here's the function (we're about to see how passwords are stored, I promise!):
Now we're getting somewhere. We create an encrypted string out of our password. I've snipped it out, but below the "sql::Statement" line, a SQL query is performed to store the encrypted data in the Login Data file. The EncryptedString function simply calls the EncryptString16 function on an Encryptor object (this just calls the following function below):
Finally! We can finally see that the password given is encrypted using a call to the Windows API function CryptProtectData. This means that the password is likely to only be recovered by a user with the same logon credential that encrypted the data. This is no problem, since malware is usually executed within the context of a user.
Decrypting the Passwords
Before talking about how to decrypt the passwords stored above, let's first take a look at the Login Data file using a sqlite browser.
Our goal will be to extract the action_url, username_value, and password_value (binary, so the SQLite browser can't display it) fields from this database. To decrypt the password, all we'll need to do is make a call to the Windows API CryptUnprotectData function. Fortunately for us, Python has a great library for making Windows API calls called pywin32.
Let's look at the PoC:
And, by running the code, we see we are successful!
While it was a bit involved to find out how the passwords are stored (other dynamic methods could be used, but I figured showing the code would be most thorough), we can see that not much effort was needed to actually decrypt the passwords. The only data that is protected is the password field, and that's only in the context of the current user.
In a previous post, I introduced a Twitter bot called dumpmon which monitors paste sites for account dumps, configuration files, and other information. Since then, I've been monitoring the information that is detected. While you can expect a follow-up post with more dumpmon-filled data soon, this post is about how browsers store passwords.
I mention dumpmon because I have started to run across quite a few pastes like this that appear to be credential logs from malware on infected computers. It got me thinking - I've always considered it best to not have browsers store passwords directly, but why? How easy can it be for malware to pull these passwords off of infected computers? Since sources are a bit tough to find in one place, I've decided to post the results here, as well as show some simple code to extract passwords from each browser's password manager.
The Browsers
For this post, I'll be analyzing the following browsers on a Windows 8 machine. Here's a table of contents for this post to help you skip to whatever browser you're interested in:
 |
| Logos by Paul Irish |
Difficulty to obtain passwords: Easy
Let's start with Chrome. Disappointingly, I found Chrome to be the easiest browser to extract passwords from. The encrypted passwords are stored in a sqlite database located at "%APPDATA%\..\Local\Google\Chrome\User Data\Default\Login Data". But how do they get there? And how is it encrypted? I got a majority of information about how passwords are stored in Chrome from this article written over 4 years ago. Since a bit has changed since then, I'll follow the same steps to show you how passwords are handled using snippets from the current Chromium source (or you justskip straight to the decryption).
Encryption and Storing Passwords
When you attempt to log into a website, Chrome first checks to see if it was a successful login:
We can see that if it's a successful login, and you used a new set of credentials that the browser didn't generate, Chrome will display a bar asking if you want your password to be remembered:
To save space, I'm omitting the code that creates the Save Password bar. However, if we click "Save password", the Accept function is called, which in turn calls the "Save" function of Chrome's password manager:
Easy enough. If it's a new login, we need to save it as such:
Again to save space, I've snipped a bit out of this (a check is performed to see if the credentials go to a Google website, etc.). After this function is called, a task is scheduled to perform the AddLoginImpl() function. This is to help keep the UI snappy:
This function attempts to call the AddLogin() function of the login database object, checking to see if it was successful. Here's the function (we're about to see how passwords are stored, I promise!):
Now we're getting somewhere. We create an encrypted string out of our password. I've snipped it out, but below the "sql::Statement" line, a SQL query is performed to store the encrypted data in the Login Data file. The EncryptedString function simply calls the EncryptString16 function on an Encryptor object (this just calls the following function below):
Finally! We can finally see that the password given is encrypted using a call to the Windows API function CryptProtectData. This means that the password is likely to only be recovered by a user with the same logon credential that encrypted the data. This is no problem, since malware is usually executed within the context of a user.
Decrypting the Passwords
Before talking about how to decrypt the passwords stored above, let's first take a look at the Login Data file using a sqlite browser.
Our goal will be to extract the action_url, username_value, and password_value (binary, so the SQLite browser can't display it) fields from this database. To decrypt the password, all we'll need to do is make a call to the Windows API CryptUnprotectData function. Fortunately for us, Python has a great library for making Windows API calls called pywin32.
Let's look at the PoC:
| 12345678910111213141516 |
|
While it was a bit involved to find out how the passwords are stored (other dynamic methods could be used, but I figured showing the code would be most thorough), we can see that not much effort was needed to actually decrypt the passwords. The only data that is protected is the password field, and that's only in the context of the current user.
Top 30 "C" programs asked in interview.
Questions
1. Write a program to find factorial of the given number...
2. Write a program to check whether the given number is even or odd.
3. Write a program to swap two numbers using a temporary variable.
4. Write a program to swap two numbers without using a temporary variable.
5. Write a program to swap two numbers using bitwise operators.
6. Write a program to find the greatest of three numbers.
7. Write a program to find the greatest among ten numbers.
8. Write a program to check whether the given number is a prime.
9. Write a program to check whether the given number is a palindrome c number.
10.Write a program to check whether the given string is a palindrome .
11.Write a program to generate the Fibonacci series.
12.Write a program to print"Hello World"without using semicolon anywhere in the code.
13.Write a program to print a semicolon without using a semicolon anywhere in the code.
14.Write a program to compare two strings without using strcmp() function.
15.Write a program to concatenat e two strings without using strcat() function.
16.Write a program to delete a specified line from a text file.
17.Write a program to replace a specified line in a text file.
18.Write a program to find the number of lines in a text file..
19.Write a C program which asks the user for a number between 1 to 9 and shows the number. If the user
inputs a number out of the specified range, the program should show an error and prompt the user for a
valid input.
20.Write a program to display the multiplica tion table of a given number..
21.WAP to check a string is Caliondrom e or not. // Maventic question.
22.WAP to print DONE,witho ut using any loop. // asked to my frnd in any company.
23.WAP to print DONE,witho ut using any loop and any conditonal clause or operators. // asked to me as a cross question of 22th question by the person i asked 22th ques.
24. WAP to find out the longest word in a string.
25.Prog of WORLD MAP. // this code was written by someone,i forgot his name,he won award for this code as short and best c code. JUST FOR FUN //
26.WAP to print the triangle of letters in increasing order of lines..
27.WAP to print'xay'in place of every'a'in a string.// DOC Update on 24-jan-12.
28.Count the Total Number of 7 comming between 1 to 100.
/* I made this code in a way that u can give Upper limit i.e. 100,Lower limit i.e. 1 and the specific number u wants to count in between i.e. 7 */ // asked by: Vishwa Pratap Rana..
29. Code for duplicate' s removal,by Amit Aru.. // Similar question was asked in Maventic 2nd round to me,,
30. WAP to find out if a given number is a power series of 2 or not,withou t any loop and without using % modulo operator.. // asked by someone on BJS..
ANSWERS
2. Write a program to check whether the given number is even or odd.
3. Write a program to swap two numbers using a temporary variable.
4. Write a program to swap two numbers without using a temporary variable.
5. Write a program to swap two numbers using bitwise operators.
6. Write a program to find the greatest of three numbers.
7. Write a program to find the greatest among ten numbers.
8. Write a program to check whether the given number is a prime.
9. Write a program to check whether the given number is a palindrome c number.
10.Write a program to check whether the given string is a palindrome .
11.Write a program to generate the Fibonacci series.
12.Write a program to print"Hello World"without using semicolon anywhere in the code.
13.Write a program to print a semicolon without using a semicolon anywhere in the code.
14.Write a program to compare two strings without using strcmp() function.
15.Write a program to concatenat e two strings without using strcat() function.
16.Write a program to delete a specified line from a text file.
17.Write a program to replace a specified line in a text file.
18.Write a program to find the number of lines in a text file..
19.Write a C program which asks the user for a number between 1 to 9 and shows the number. If the user
inputs a number out of the specified range, the program should show an error and prompt the user for a
valid input.
20.Write a program to display the multiplica tion table of a given number..
21.WAP to check a string is Caliondrom e or not. // Maventic question.
22.WAP to print DONE,witho ut using any loop. // asked to my frnd in any company.
23.WAP to print DONE,witho ut using any loop and any conditonal clause or operators. // asked to me as a cross question of 22th question by the person i asked 22th ques.
24. WAP to find out the longest word in a string.
25.Prog of WORLD MAP. // this code was written by someone,i forgot his name,he won award for this code as short and best c code. JUST FOR FUN //
26.WAP to print the triangle of letters in increasing order of lines..
27.WAP to print'xay'in place of every'a'in a string.// DOC Update on 24-jan-12.
28.Count the Total Number of 7 comming between 1 to 100.
/* I made this code in a way that u can give Upper limit i.e. 100,Lower limit i.e. 1 and the specific number u wants to count in between i.e. 7 */ // asked by: Vishwa Pratap Rana..
29. Code for duplicate' s removal,by Amit Aru.. // Similar question was asked in Maventic 2nd round to me,,
30. WAP to find out if a given number is a power series of 2 or not,withou t any loop and without using % modulo operator.. // asked by someone on BJS..
ANSWERS
````````
1. Write a program to find factorial of the given number.
Recursion: A function is called'recursive 'if a statement within the body of a function calls the same function. It
is also called'circular definition '. Recursion is thus a process of defining something in terms of itself.
Program: To calculate the factorial value using recursion.
#include
int fact(int n);
int main(){
int x, i;
printf("En ter a value for x: \n");
scanf("%d" ,&x);
i = fact(x);
printf("\n Factorial of %d is %d", x, i);
return 0;
}int fact(int n){
/* n=0 indicates a terminatin g condition */
if (n
return (1);
}else{
/* function calling itself */
return (n * fact(n - 1));
/*n*fact(n -1) is a recursive expression */
}
}
Output:
Enter a value for x:
4
Factorial of 4 is 24
Explanatio n:
fact(n) = n * fact(n-1)
If n=4
fact(4) = 4 * fact(3) there is a call to fact(3)
fact(3) = 3 * fact(2)
fact(2) = 2 * fact(1)
fact(1) = 1 * fact(0)
fact(0) = 1
fact(1) = 1 * 1 = 1
fact(2) = 2 * 1 = 2
fact(3) = 3 * 2 = 6
Thus fact(4) = 4 * 6 = 24
Terminatin g condition( n
infinite loop.
2. Write a program to check whether the given number is even or odd.
Program:
#include
int main(){
int a;
printf("En ter a: \n");
scanf("%d" ,&a);
/* logic */
if (a % 2 == 0){
printf("Th e given number is EVEN\n");
}
else{
printf("Th e given number is ODD\n");
}
return 0;
}
Output:
Enter a: 2
The given number is EVEN
Explanatio n with examples:
Example 1: If entered number is an even number
Let value of'a'entered is 4
if(a%2==0) then a is an even number, else odd.
i.e. if(4%2==0) then 4 is an even number, else odd.
To check whether 4 is even or odd, we need to calculate (4%2).
/* % (modulus) implies remainder value. */
/* Therefore if the remainder obtained when 4 is divided by 2 is 0, then 4 is even. */
4%2==0 is true
Thus 4 is an even number.
Example 2: If entered number is an odd number.
Let value of'a'entered is 7
if(a%2==0) then a is an even number, else odd.
i.e. if(7%2==0) then 4 is an even number, else odd.
To check whether 7 is even or odd, we need to calculate (7%2).
7%2==0 is false /* 7%2==1 condition fails and else part is executed */
Thus 7 is an odd number.
3. Write a program to swap two numbers using a temporary variable.
Swapping interchang es the values of two given variables.
Logic:
step1: temp=x;
step2: x=y;
step3: y=temp;
Example:
if x=5 and y=8, consider a temporary variable temp.
step1: temp=x=5;
step2: x=y=8;
step3: y=temp=5;
Thus the values of the variables x and y are interchang ed.
Program:
#include
int main(){
int a, b, temp;
printf("En ter the value of a and b: \n");
scanf("%d %d",&a,&b);
printf("Be fore swapping a=%d, b=%d \n", a, b);
/*Swapping logic */
temp = a;
a = b;
b = temp;
printf("Af ter swapping a=%d, b=%d", a, b);
return 0;
}
Output:
Enter the values of a and b: 2 3
Before swapping a=2, b=3
After swapping a=3, b=2
4. Write a program to swap two numbers without using a temporary variable.
Swapping interchang es the values of two given variables.
Logic:
step1: x=x+y;
step2: y=x-y;
step3: x=x-y;
Example:
if x=7 and y=4
step1: x=7+4=11;
step2: y=11-4=7;
step3: x=11-7=4;
Thus the values of the variables x and y are interchang ed.
Program:
#include
int main(){
int a, b;
printf("En ter values of a and b: \n");
scanf("%d %d",&a,&b);
printf("Be fore swapping a=%d, b=%d\n", a,b);
/*Swapping logic */
a = a + b;
b = a - b;
a = a - b;
printf("Af ter swapping a=%d b=%d\n", a, b);
return 0;
}
Output:
Enter values of a and b: 2 3
Before swapping a=2, b=3
The values after swapping are a=3 b=2
5. Write a program to swap two numbers using bitwise operators.
Program:
#include
int main(){
int i = 65;
int k = 120;
printf("\n value of i=%d k=%d before swapping", i, k);
i = i ^ k;
k = i ^ k;
i = i ^ k;
printf("\n value of i=%d k=%d after swapping", i, k);
return 0;
}
Explanatio n:
i = 65; binary equivalent of 65 is 0100 0001
k = 120; binary equivalent of 120 is 0111 1000
i = i^k;
i...0100 0001
k...0111 1000
---------
val of i = 0011 1001
---------
k = i^k
i...0011 1001
k...0111 1000
---------
val of k = 0100 0001 binary equivalent of this is 65
---------( that is the initial value of i)
i = i^k
i...0011 1001
k...0100 0001
---------
val of i = 0111 1000 binary equivalent of this is 120
--------- (that is the initial value of k)
6. Write a program to find the greatest of three numbers.
Program:
#include
int main(){
int a, b, c;
printf("En ter a,b,c: \n");
scanf("%d %d %d",&a,&b,&c);
if (a>b&&a>c){
printf("a is Greater than b and c");
}
else if (b>a&&b>c){
printf("b is Greater than a and c");
}
else if (c>a&&c>b){
printf("c is Greater than a and b");
}
else{
printf("al l are equal or any two values are equal");
}
return 0;
}
Output:
Enter a,b,c: 3 5 8
c is Greater than a and b
Explanatio n with examples:
Consider three numbers a=5,b=4,c= 8
if(a>b&&a>c) then a is greater than b and c
now check this condition for the three numbers 5,4,8 i.e.
if(5>4&&5>8) /* 5>4 is true but 5>8 fails */
so the control shifts to else if condition
else if(b>a&&b>c) then b is greater than a and c
now checking this condition for 5,4,8 i.e.
else if(4>5&&4>8) / * both the conditions fail */
now the control shifts to the next else if condition
else if(c>a&&c>b) then c is greater than a and b
now checking this condition for 5,4,8 i.e.
else if(8>5&&8>4) / * both conditions are satisfied */
Thus c is greater than a and b.
7. Write a program to find the greatest among ten numbers.
Program:
#include
int main(){
int a[10];
int i;
int greatest;
printf("En ter ten values:");
//Store 10 numbers in an array
for (i = 0; i scanf("%d" ,&a[i]);
}
//Assume that a[0] is greatest
greatest = a[0];
for (i = 0; i if (a[i]>greatest){
greatest = a[i];
}
}
printf("\n Greatest of ten numbers is %d", greatest);
return 0;
}
Output:
Enter ten values: 2 53 65 3 88 8 14 5 77 64 Greatest of ten numbers is 88
Explanatio n with example:
Entered values are 2, 53, 65, 3, 88, 8, 14, 5, 77, 64
They are stored in an array of size 10. let a[] be an array holding these values.
/* how the greatest among ten numbers is found */
Let us consider a variable'greatest' . At the beginning of the loop, variable'greatest' is assinged with the value of
first element in the array greatest=a [0]. Here variable'greatest' is assigned 2 as a[0]=2.
Below loop is executed until end of the array'a[]';.
for(i=0; i
{
if(a[i]>gr eatest)
{
greatest= a[i];
}
}
For each value of'i', value of a[i] is compared with value of variable'greatest' . If any value greater than the value
of'greatest' is encountere d, it would be replaced by a[i]. After completion of'for'loop, the value of variable
'greatest' holds the greatest number in the array. In this case 88 is the greatest of all the numbers.
8. Write a program to check whether the given number is a prime.
A prime number is a natural number that has only one and itself as factors. Examples: 2, 3, 13 are prime
numbers.
Program:
#include
main(){
int n, i, c = 0;
printf("En ter any number n: \n");
scanf("%d" ,&n);
/*logic*/
for (i = 1; i
if (n % i == 0){
c++;
}
}
if (c == 2){
printf("n is a Prime number");
}
else{
printf("n is not a Prime number");
}
return 0;
}
Output:
Enter any number n: 7
n is Prime
Explanatio n with examples:
consider a number n=5
for(i=0;i
i.e. for(i=0;i
1st iteration: i=1;i
here i is incremente d i.e. i value for next iteration is 2
now if(n%i==0) then c is incremente d
i.e.if(5%1 ==0)then c is incremente d, here 5%1=0 thus c is incremente d.
now c=1;
2nd iteration: i=2;i
here i is incremente d i.e. i value for next iteration is 3
now if(n%i==0) then c is incremente d
i.e.if(5%2 ==0) then c is incremente d, but 5%2!=0 and so c is not incremente d, c remains 1
c=1;
3rd iteration: i=3;i
here i is incremente d i.e. i value for next iteration is 4
now if(n%i==0) then c is incremente d
i.e.if(5%3 ==0) then c ic incremente d, but 5%3!=0 and so c is not incremente d, c remains 1
c=1;
4th iteration: i=4;i
here i is incremente d i.e. i value for next iteration is 5
now if(n%i==0) then c is incremente d
i.e. if(5%4==0) then c is incremente d, but 5%4!=0 and so c is not incremente d, c remains 1
c=1;
5th iteration: i=5;i
here i is incremente d i.e. i value for next iteration is 6
now if(n%i==0) then c is incremente d
i.e. if(5%5==0) then c is incremente d, 5%5=0 and so c is incremente d.
i.e. c=2
6th iteration: i=6;i
here i value is 6 and 6
now if(c==2) then n is a prime number
we have c=2 from the 5th iteration and thus n=5 is a Prime number.
9. Write a program to check whether the given number is a palindromi c number.
If a number, which when read in both forward and backward way is same, then such a number is called a
palindrome number.
Program:
#include
int main(){
int n, n1, rev = 0, rem;
printf("En ter any number: \n");
scanf("%d" ,&n);
n1 = n;
/* logic */
while (n>0){
rem = n % 10;
rev = rev * 10 + rem;
n = n / 10;
}
if (n1 == rev){
printf("Gi ven number is a palindromi c number");
}
else{
printf("Gi ven number is not a palindromi c number");
}
return 0;
}
Output:
Enter any number: 121
Given number is a palindrome
Explanatio n with an example:
Consider a number n=121, reverse=0, remainder;
number=121
now the while loop is executed /* the condition (n>0) is satisfied */
/* calculate remainder */
remainder of 121 divided by 10=(121%10 )=1;
now reverse=(r everse*10) +remainder
=(0*10)+1 / * we have initialized reverse=0 */
=1
number=num ber/10
=121/10
=12
now the number is 12, greater than 0. The above process is repeated for number=12.
remainder= 12%10=2;
reverse=(1 *10)+2=12;
number=12/ 10=1;
now the number is 1, greater than 0. The above process is repeated for number=1.
remainder= 1%10=1;
reverse=(1 2*10)+1=12 1;
number=1/ 10 / * the condition n>0 is not satisfied,co ntrol leaves the while loop */
Program stops here. The given number=121 equals the reverse of the number. Thus the given number is a
palindrome number.
10.Write a program to check whether the given string is a palindrome .
Palindrome is a string, which when read in both forward and backward way is same.
Example: radar, madam, pop, lol, rubber, etc.,
Program:
#include
#include
int main(){
char string1[20 ];
int i, length;
int flag = 0;
printf("En ter a string: \n");
scanf("%s" , string1);
length = strlen(str ing1);
for(i=0;i<length> if(string1 [i] != string1[le ngth-i-1]) {
flag = 1;
break;
}
}
if (flag){
printf("%s is not a palindrome \n", string1);
}
else{
printf("%s is a palindrome \n", string1);
}
return 0;
}
Output:
Enter a string: radar
"radar"is a palindrome
Explanatio n with example:
To check if a string is a palindrome or not, a string needs to be compared with the reverse of itself.
Consider a palindrome string:"radar",
---------- ---------- -------
index: 0 1 2 3 4
value: r a d a r
---------- ---------- -------
To compare it with the reverse of itself, the following logic is used:
0th character in the char array, string1 is same as 4th character in the same string.
1st character is same as 3rd character.
2nd character is same as 2nd character.
. . . .
ith character is same as'length-i- 1'th character.
If any one of the above condition fails, flag is set to true(1), which implies that the string is not a palindrome .
By default, the value of flag is false(0). Hence, if all the conditions are satisfied, the string is a palindrome .
11.Write a program to generate the Fibonacci series.
Fibonacci series: Any number in the series is obtained by adding the previous two numbers of the series.
Let f(n) be n'th term.
f(0)=0;
f(1)=1;
f(n)=f(n-1 )+f(n-2); (for n>=2)
Series is as follows
011
(1+0)
2 (1+1)
3 (1+2)
5 (2+3)
8 (3+5)
13 (5+8)
21 (8+13)
34 (13+21)
...and so on
Program: to generate Fibonacci Series(10 terms)
#include
int main(){
//array fib stores numbers of fibonacci series
int i, fib[25];
// initialized first element to 0
fib[0] = 0;
// initialized second element to 1
fib[1] = 1;
//loop to generate ten elements
for (i = 2; i //i'th element of series is equal to the sum of i-1'th element and i-2'th element.
fib[i] = fib[i - 1] + fib[i - 2];
}
printf("Th e fibonacci series is as follows \n");
//print all numbers in the series
for (i = 0; i printf("%d \n", fib[i]);
}
return 0;
}
Output:
The fibonacci series is as follows
01123581
3
21
34
Explanatio n:
The first two elements are initialize d to 0, 1 respective ly. Other elements in the series are generated by looping
and adding previous two numbes. These numbers are stored in an array and ten elements of the series are
printed as output.
12.Write a program to print"Hello World"without using semicolon anywhere in the code.
Generally when we use printf("") statement, we have to use a semicolon at the end. If printf is used inside an if
Condition, semicolon can be avoided.
Program: Program to print something without using semicolon (;)
#include
int main(){
//printf returns the length of string being printed
if (printf("H ello World\n")) //prints Hello World and returns 11
{
//do nothing
}
return 0;
}
Output:
Hello World
Explanatio n:
The if statement checks for condition whether the return value of printf("He llo World") is greater than 0. printf
function returns the length of the string printed. Hence the statement if (printf("H ello World")) prints the string
"Hello World".
13.Write a program to print a semicolon without using a semicolon anywhere in the code.
Generally when use printf("") statement we have to use semicolon at the end.
If we want to print a semicolon, we use the statement: printf(";" );
In above statement, we are using two semicolons . The task of printing a semicolon without using semicolon anywhere in the code can be accomplish ed by using the ascii value of';'which is equal to 59.
Program: Program to print a semicolon without using semicolon in the code.
#include
int main(void) {
//prints the character with ascii value 59, i.e., semicolon
if (printf("% c\n", 59)){
//prints semicolon
}
return 0;
}
Output:
;
Explanatio n:
If statement checks whether return value of printf function is greater than zero or not. The return value of function
call printf("%c ",59) is 1. As printf returns the length of the string printed. printf("%c ",59) prints ascii value that
correspond s to 59, that is semicolon( .
14.Write a program to compare two strings without using strcmp() function.
strcmp() function compares two strings lexicograp hically. strcmp is declared in stdio.h
Case 1: when the strings are equal, it returns zero.
Case 2: when the strings are unequal, it returns the difference between ascii values of the characters that differ.
a) When string1 is greater than string2, it returns positive value.
b) When string1 is lesser than string2, it returns negative value.
Syntax:
int strcmp (const char *s1, const char *s2);
Program: to compare two strings.
#include
#include
int cmpstr(cha r s1[10], char s2[10]);
int main(){
char arr1[10] ="Nodalo";
char arr2[10] ="nodalo";
printf("%d", cmpstr(arr 1, arr2));
// cmpstr() is equivalent of strcmp()
return 0;
}/
/s1, s2 are strings to be compared
int cmpstr(cha r s1[10], char s2[10]){
//strlen function returns the length of argument string passed
int i = strlen(s1) ;
int k = strlen(s2) ;
int bigger;
if (i<k> bigger = k;
}
else if (i>k){
bigger = i;
}
else{
bigger = i;
}
//loops'bigger'times
for (i = 0; i<bigger i=""> // if ascii values of characters s1[i], s2[i] are equal do nothing
if (s1[i] == s2[i]){
}
//else return the ascii difference
else{
return (s1[i] - s2[i]);
}
}
//return 0 when both strings are same
//This statement is executed only when both strings are equal
return (0);
}
Output:
-32
Explanatio n:
cmpstr() is a function that illustrate s C standard function strcmp(). Strings to be compared are sent as arguments
to cmpstr().
Each character in string1 is compared to its correspond ing character in string2. Once the loop encounters a
differing character in the strings, it would return the ascii difference of the differing characters and exit.
15.Write a program to concatenat e two strings without using strcat() function.
strcat(str ing1,strin g2) is a C standard function declared in the header file string.h
The strcat() function concatenat es string2, string1 and returns string1.
Program: Program to concatenat e two strings
#include
#include
char *strct(cha r *c1, char *c2);
char *strct(cha r *c1, char *c2){
//strlen function returns length of argument string
int i = strlen(c1) ;
int k = 0;
// loops until null is encountered and appends string c2 to c1
while (c2[k] !='\0'){
c1[i + k] = c2[k];
k++;
}
return c1;
}
int main(){
char string1[15 ] ="first";
char string2[15 ] ="second";
char *finalstr;
printf("Be fore concatenat ion:"
"\n string1 = %s \n string2 = %s", string1, string2);
// addresses of string1, string2 are passed to strct()
finalstr = strcat(str ing1, string2);
printf("\n After concatenat ion:");
//prints the contents of string whose address is in finalstr
printf("\n finalstr = %s", finalstr);
//prints the contents of string1
printf("\n string1 = %s", string1);
//prints the contents of string2
printf("\n string2 = %s", string2);
return 0;
}
Output:
Before concatenat ion:
string1 = first
string2 = second
After concatenat ion:
finalstr = firstsecon d
string1 = firstsecon d
string2 = second
Explanatio n:
string2 is appended at the end of string1 and contents of string2 are unchanged.
In strct() function, using a for loop, all the characters of string'c2'are copied at the end of c1. return (c1) is
equivalent to return&c1[0] and it returns the base address of'c1'.'finalstr' stores that address returned by the
function strct().
16.Write a program to delete a specified line from a text file.
In this program, user is asked for a filename he needs to change. User is also asked for the line number that is
to be deleted. The filename is stored in'filename' . The file is opened and all the data is transferre d to another file
except that one line the user specifies to delete.
Program: Program to delete a specific line.
#include
int main(){
FILE *fp1, *fp2;
// consider 40 character string to store filename
char filename[4 0];
char c;
int del_line, temp = 1;
//asks user for file name
printf("En ter file name:");
// receives file name from user and stores in'filename'
scanf("%s" , filename);
//open file in read mode
fp1 = fopen(file name,"r");
c = getc(fp1);
//until the last character of file is obtained
while (c != EOF)
{
printf("%c ", c);
//print current character and read next character
c = getc(fp1);
}
//rewind
rewind(fp1 );
printf("\n Enter line number of the line to be deleted:") ;
//accept number from user.
scanf("%d" ,&del_line) ;
//open new file in write mode
fp2 = fopen("cop y.c","w");
c = getc(fp1);
while (c != EOF){
c = getc(fp1);
if (c =='\n')
temp++;
//except the line to be deleted
if (temp != del_line)
{
//copy all lines in file copy.c
putc(c, fp2);
}
}
//close both the files.
fclose(fp1 );
fclose(fp2 );
//remove original file
remove(fil ename);
//rename the file copy.c to original name
rename("co py.c", filename);
printf("\n The contents of file after being modified are as follows:\n ");
fp1 = fopen(file name,"r");
c = getc(fp1);
while (c != EOF){
printf("%c ", c);
c = getc(fp1);
}
fclose(fp1 );
return 0;
}
Output:
Enter file name:abc.t xt
hi.
Hello
how are you?
I am fine
hope the same
Enter line number of the line to be deleted:4
The contents of file after being modified are as follows:
hi.
hello
how are you?
hope the same
Explanatio n:
In this program, user is asked for a filename that needs to be modified. Entered file name is stored in a char
array'filename' . This file is opened in read mode using file pointer'fp1'. Character'c'is used to read characters
from the file and print them to the output. User is asked for the line number in the file to be deleted. The file
pointer is rewinded back and all the lines of the file except for the line to be deleted are copied into another file
"copy.c". Now"copy.c"is renamed to the original filename. The original file is opened in read mode and the
modified contents of the file are displayed on the screen.
17.Write a program to replace a specified line in a text file.
Program: Program to replace a specified line in a text file.
#include
int main(void) {
FILE *fp1, *fp2;
// 'filename'i s a 40 character string to store filename
char filename[4 0];
char c;
int del_line, temp = 1;
//asks user for file name
printf("En ter file name:");
// receives file name from user and stores in'filename'
scanf("%s" , filename);
fp1 = fopen(file name,"r");
//open file in read mode
c = getc(fp1);
//print the contents of file .
while (c != EOF){
printf("%c ", c);
c = getc(fp1);
}
//ask user for line number to be deleted.
printf("\n Enter line number to be deleted and replaced") ;
scanf("%d" ,&del_line) ;
//take fp1 to start point.
rewind(fp1 );
//open copy.c in write mode
fp2 = fopen("cop y.c","w");
c = getc(fp1);
while (c != EOF){
if (c =='\n'){
temp++;
}
// till the line to be deleted comes,copy the content from one file to other
if (temp != del_line){
putc(c, fp2);
}
else //when the line to be deleted comes
{
while ((c = getc(fp1)) !='\n'){
}
//read and skip the line ask for new text
printf("En ter new text");
//flush the input stream
fflush(std in);
putc('\n', fp2);
//put'\n'in new file
while ((c = getchar()) !='\n')
putc(c, fp2);
//take the data from user and place it in new file
fputs("\n" , fp2);
temp++;
}
// continue this till EOF is encountere d
c = getc(fp1);
}
//close both files
fclose(fp1 );
fclose(fp2 );
//remove original file
remove(fil ename);
//rename new file with old name opens the file in read mode
rename("co py.c", filename);
fp1 = fopen(file name,"r");
//reads the character from file
c = getc(fp1);
// until last character of file is encountered
while (c != EOF){
printf("%c ", c);
// all characters are printed
c = getc(fp1);
}
//close the file pointer
fclose(fp1 );
return 0;
}
Output:
Enter file name:abc.t xt
hi.
hello
how are you?
hope the same
Enter line number of the line to be deleted and replaced:4
Enter new text: sayonara see you soon
hi.
hello
how are you?
sayonara see you soon
Explanatio n:
In this program, the user is asked to type the name of the file. The File by name entered by user is opened in
read mode. The line number of the line to be replaced is asked as input. Next the data to be replaced is asked. A
new file is opened in write mode named"copy.c". Now the contents of original file are transferre d into new file
and the line to be modified is deleted. New data is stored in its place and remaining lines of the original file are
also transferre d. The copied file with modified contents is replaced with the original file's name. Both the file
pointers are closed and the original file is again opened in read mode and the contents of the original file is
printed as output.
18.Write a program to find the number of lines in a text file.
Number of lines in a file can be determined by counting the number of new line characters present.
Program: Program to count number of lines in a file.
#include
int main()
/* Ask for a filename and count number of lines in the file*/
{
//a pointer to a FILE structure
FILE *fp;
int no_lines = 0;
// consider 40 character string to store filename
char filename[4 0], sample_chr ;
//asks user for file name
printf("En ter file name:");
// receives file name from user and stores in a string named'filename'
scanf("%s" , filename);
//open file in read mode
fp = fopen(file name,"r");
//get character from file and store in sample_chr
sample_chr = getc(fp);
while (sample_ch r != EOF){
// Count whenever sample_chr is'\n'(new line) is encountere d
if (sample_ch r =='\n')
{
// increment variable'no_lines' by 1
no_lines=n o_lines+1;
}
//take next character from file.
sample_chr = getc(fp);
}
fclose(fp) ; //close file.
printf("Th ere are %d lines in %s \n", no_lines, filename);
return 0;
}
Output:
Enter file name:abc.t xt
There are 4 lines in abc.txt
Explanatio n:
In this program, name of the file to be read is taken as input. A file by the given name is opened in read-mode
using a File pointer'fp'. Characters from the file are read into a char variable'sample_ch r'with the help of getc
function. If a new line character( '\n') is encountere d, the integer variable'no_lines' is incremente d. If the
character read into'sample_ch ar'is not a new line character, next character is read from the file. This process is
continued until the last character of the file(EOF) is encountere d. The file pointer is then closed and the total
number of lines is shown as output.
19.Write a C program which asks the user for a number between 1 to 9 and shows the number. If the
user inputs a number out of the specified range, the program should show an error and prompt
the user for a valid input.
Program: Program for accepting a number in a given range.
#include
int getnumber( );
int main(){
int input = 0;
//call a function to input number from key board
input = getnumber( );
//when input is not in the range of 1 to 9,print error message
while (!((input = 1))){
printf("[E RROR] The number you entered is out of range");
//input another number
input = getnumber( );
}
//this function is repeated until a valid input is given by user.
printf("\n The number you entered is %d", input);
return 0;
}/
/this function returns the number given by user
int getnumber( ){
int number;
//asks user for a input in given range
printf("\n Enter a number between 1 to 9 \n");
scanf("%d" ,&number);
return (number);
}
Output:
Enter a number between 1 to 9
45
[ERROR] The number you entered is out of range
Enter a number between 1 to 9
4
The number you entered is 4
Explanatio n:
getfunctio n() function accepts input from user.'while'loop checks whether the number falls within range or not
and accordingl y either prints the number(If the number falls in desired range) or shows error message(nu mber is
out of range).
20.Write a program to display the multiplica tion table of a given number.
Program: Multiplica tion table of a given number
#include
int main(){
int num, i = 1;
printf("\n Enter any Number:");
scanf("%d" ,&num);
printf("Mu ltiplicati on table of %d: \n", num);
while (i
printf("\n %d x %d = %d", num, i, num * i);
i++;
}
return 0;
}
Output:
Enter any Number:5
5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50
Explanatio n:
We need to multiply the given number (i.e. the number for which we want the multiplica tion table)
with value of'i'which increments from 1 to 10.
21. .WAP to check a string is Caliondrom e or not. // Maventic question.
#include
#include
void main()
{
int i,j=0; char a[100];
clrscr();
printf("\n Enter the string to check for caliondrom e:\n");
gets(a);
if(strlen( a)%6)
{
printf("\n %s: is Not a caliondrom e..",a);
getch();
exit(0);
}
for (i=0;a[i]! ='\0'
{
if((a[i]== a[i+5])&&( a[i+1]==a[ i+4])&&(a[ i+2]==a[i+ 3]))
i=i+6;
else
{
j=1;
break;
}
}
if(j)
printf("\n %s: is Not a caliondrom e..",a);
else
printf("\n %s: is a caliondrom e..",a);
getch();
}
22.WAP to print DONE,witho ut using any loop. // asked to my frnd in many company.
#include
void main()
{
static int i=0;
printf("\n %d. DONE",i);
if(i++
main();
getch();
exit(0); / * I used exit(0) to terminate the program after 100 DONE,,i dunno why it was not terminating without using it,may be just at my system,try without it at ur sustem,it sud work */
}
23.WAP to print DONE,witho ut using any loop and any conditonal clause or operators.
/* This code is just in purpose to solve the above question,, but its not a good code in programmin g,as its terminatin g at divide error,,if anyone have a better code,let me know */
main()
{
static int i=100;
printf("%d . DONE\n",10 1-i);
main(1/ --i);
}
/* use"ctrl+f9",then"alt+f5"to see the result */
24. WAP to find out the longest word in a string.
#include
#include
#include
void main()
{
int i,max=0,co unt=0,j;
char str[100]; / * ={"INDIA IS DEMOCRATIC COUNTRY"}; u can use a string inside,in place of user input */
printf("\n Enter the string\n:" );
gets(str);
for(i=0;i
{
if(!(str[i ]==32))
{
count++;
}
else
{
if(max
{
j=i-count;
max=count;
}
count=0;
}
}
for(i=j;i
printf("%c ",str[i]);
getch();
}
25.Prog of WORLD MAP.
#include main(l ,a,n,d)cha r**a;{for(d=atoi (a[1])/ 10*80- atoi(a[2]) / 5-596;n="@N KA\CLCCGZA AQBEAADAFa ISADJABBA^ \SNLGAQABD AXIMBAACTB ATAHDBAN\Z cEMMCCCCAA hEIJFAEAAA BAfHJE\TBd FLDAANEfDN BPHdBcBBBE A_AL\ H E L L O, W O R L D!"[l++-3];)f or(;n-->64 putchar(!d +++33^ l&1);print f("\n\n\n\ n\t\tFound By:\n\t\t\ t Amit Aru");getc h();}
26.WAP to print the triangle of letters in increasing order of lines.
#include
#include
void main()
{
int i,j,k;
char ch;
printf("\n Enter the number of lines wants to make the triangle \n:");
scanf("%d" ,&i);
for(j=1;j
{
ch=65;
for(k=1;k
{
printf("%c ",ch++);
}
printf("\n ");
}
getch();
}
27.WAP to print'xay'in place of every'a'in a string.
#include
#include
void main()
{
int i=0;
char str[100],x ='x',y='y' ;
printf("En ter the string\n:");
gets(str);
while(str[ i]!='\0')
{
if(str[i]= ='a')
{
printf("%c ",x);
printf("%c ",str[i++] );
printf("%c ",y);
}
else
{
printf("%c ",str[i++] );
}
}
getch();
}
28.Count the Total Number of 7 comming between 1 to 100.
/* I made this code in a way that u can give Upper limit i.e. 100,Lower limit i.e. 1 and the specific number u wants to count in between i.e. 7 */
#include
#include
void main()
{
int i,j,U=100, L=1,count= 0,r=1,n;
clrscr();
printf("\n Enter the number u wants to count\n:");
scanf("%d" ,&n);
printf("\n Enter the lower limit\n:");
scanf("%d" ,&L);
printf("\n Enter the upper limit\n:");
scanf("%d" ,&U);
for (i=L;i
{
j=i;
while(j)
{
r=j%10;
if (r==n)
{
count++;
}
j=j/10;
}
}
if(n==0&&L ==0)
count++;
printf("\n Total Number of %d between %d and %d = %d",n,L,U, count);
getch();
}
29. Code for duplicate' s removal,by Amit Aru.
#include
#include
void main()
{
int i,j,k=0,co unt[300]={ 0};
char ch,str[100 0],str1[10 00];
clrscr();
printf("\n Enter the string to remove duplicasy\ n:");
gets(str);
for (i=0;str[i ]!='\0';i+ +)
{
ch=str[i];
count['']=0; / * U can use other delimiter inplace of space''here,just put that char inside'',for ex: count['A']=0 ; if u dnt want any delimiter, just remove this line.*/
if(count[c h])
continue;
else
{
str1[k++]= ch;
count[ch]= 1;
}
}
puts(str1) ;
getch();
}
30. WAP to find out if a given number is a power series of 2 or not,withou t any loop and without using % modulo operator.
#include
#include
int pow2(float );
void main()
{
int i,flag;
clrscr();
printf("En ter the number\n") ;
scanf("%d" ,&i);
flag=pow2( i);
if(flag)
printf("\n %d is power series of 2",i);
else
printf("\n %d is not a power series of 2",i);
getch();
}
int pow2(float j)
{
static float x;
x=j/2;
if(x==2)
return 1;
if(x
return 0;
x=pow2(x);
}
</bigger></k></length>
1. Write a program to find factorial of the given number.
Recursion: A function is called'recursive 'if a statement within the body of a function calls the same function. It
is also called'circular definition '. Recursion is thus a process of defining something in terms of itself.
Program: To calculate the factorial value using recursion.
#include
int fact(int n);
int main(){
int x, i;
printf("En ter a value for x: \n");
scanf("%d" ,&x);
i = fact(x);
printf("\n Factorial of %d is %d", x, i);
return 0;
}int fact(int n){
/* n=0 indicates a terminatin g condition */
if (n
return (1);
}else{
/* function calling itself */
return (n * fact(n - 1));
/*n*fact(n -1) is a recursive expression */
}
}
Output:
Enter a value for x:
4
Factorial of 4 is 24
Explanatio n:
fact(n) = n * fact(n-1)
If n=4
fact(4) = 4 * fact(3) there is a call to fact(3)
fact(3) = 3 * fact(2)
fact(2) = 2 * fact(1)
fact(1) = 1 * fact(0)
fact(0) = 1
fact(1) = 1 * 1 = 1
fact(2) = 2 * 1 = 2
fact(3) = 3 * 2 = 6
Thus fact(4) = 4 * 6 = 24
Terminatin g condition( n
infinite loop.
2. Write a program to check whether the given number is even or odd.
Program:
#include
int main(){
int a;
printf("En ter a: \n");
scanf("%d" ,&a);
/* logic */
if (a % 2 == 0){
printf("Th e given number is EVEN\n");
}
else{
printf("Th e given number is ODD\n");
}
return 0;
}
Output:
Enter a: 2
The given number is EVEN
Explanatio n with examples:
Example 1: If entered number is an even number
Let value of'a'entered is 4
if(a%2==0) then a is an even number, else odd.
i.e. if(4%2==0) then 4 is an even number, else odd.
To check whether 4 is even or odd, we need to calculate (4%2).
/* % (modulus) implies remainder value. */
/* Therefore if the remainder obtained when 4 is divided by 2 is 0, then 4 is even. */
4%2==0 is true
Thus 4 is an even number.
Example 2: If entered number is an odd number.
Let value of'a'entered is 7
if(a%2==0) then a is an even number, else odd.
i.e. if(7%2==0) then 4 is an even number, else odd.
To check whether 7 is even or odd, we need to calculate (7%2).
7%2==0 is false /* 7%2==1 condition fails and else part is executed */
Thus 7 is an odd number.
3. Write a program to swap two numbers using a temporary variable.
Swapping interchang es the values of two given variables.
Logic:
step1: temp=x;
step2: x=y;
step3: y=temp;
Example:
if x=5 and y=8, consider a temporary variable temp.
step1: temp=x=5;
step2: x=y=8;
step3: y=temp=5;
Thus the values of the variables x and y are interchang ed.
Program:
#include
int main(){
int a, b, temp;
printf("En ter the value of a and b: \n");
scanf("%d %d",&a,&b);
printf("Be fore swapping a=%d, b=%d \n", a, b);
/*Swapping logic */
temp = a;
a = b;
b = temp;
printf("Af ter swapping a=%d, b=%d", a, b);
return 0;
}
Output:
Enter the values of a and b: 2 3
Before swapping a=2, b=3
After swapping a=3, b=2
4. Write a program to swap two numbers without using a temporary variable.
Swapping interchang es the values of two given variables.
Logic:
step1: x=x+y;
step2: y=x-y;
step3: x=x-y;
Example:
if x=7 and y=4
step1: x=7+4=11;
step2: y=11-4=7;
step3: x=11-7=4;
Thus the values of the variables x and y are interchang ed.
Program:
#include
int main(){
int a, b;
printf("En ter values of a and b: \n");
scanf("%d %d",&a,&b);
printf("Be fore swapping a=%d, b=%d\n", a,b);
/*Swapping logic */
a = a + b;
b = a - b;
a = a - b;
printf("Af ter swapping a=%d b=%d\n", a, b);
return 0;
}
Output:
Enter values of a and b: 2 3
Before swapping a=2, b=3
The values after swapping are a=3 b=2
5. Write a program to swap two numbers using bitwise operators.
Program:
#include
int main(){
int i = 65;
int k = 120;
printf("\n value of i=%d k=%d before swapping", i, k);
i = i ^ k;
k = i ^ k;
i = i ^ k;
printf("\n value of i=%d k=%d after swapping", i, k);
return 0;
}
Explanatio n:
i = 65; binary equivalent of 65 is 0100 0001
k = 120; binary equivalent of 120 is 0111 1000
i = i^k;
i...0100 0001
k...0111 1000
---------
val of i = 0011 1001
---------
k = i^k
i...0011 1001
k...0111 1000
---------
val of k = 0100 0001 binary equivalent of this is 65
---------( that is the initial value of i)
i = i^k
i...0011 1001
k...0100 0001
---------
val of i = 0111 1000 binary equivalent of this is 120
--------- (that is the initial value of k)
6. Write a program to find the greatest of three numbers.
Program:
#include
int main(){
int a, b, c;
printf("En ter a,b,c: \n");
scanf("%d %d %d",&a,&b,&c);
if (a>b&&a>c){
printf("a is Greater than b and c");
}
else if (b>a&&b>c){
printf("b is Greater than a and c");
}
else if (c>a&&c>b){
printf("c is Greater than a and b");
}
else{
printf("al l are equal or any two values are equal");
}
return 0;
}
Output:
Enter a,b,c: 3 5 8
c is Greater than a and b
Explanatio n with examples:
Consider three numbers a=5,b=4,c= 8
if(a>b&&a>c) then a is greater than b and c
now check this condition for the three numbers 5,4,8 i.e.
if(5>4&&5>8) /* 5>4 is true but 5>8 fails */
so the control shifts to else if condition
else if(b>a&&b>c) then b is greater than a and c
now checking this condition for 5,4,8 i.e.
else if(4>5&&4>8) / * both the conditions fail */
now the control shifts to the next else if condition
else if(c>a&&c>b) then c is greater than a and b
now checking this condition for 5,4,8 i.e.
else if(8>5&&8>4) / * both conditions are satisfied */
Thus c is greater than a and b.
7. Write a program to find the greatest among ten numbers.
Program:
#include
int main(){
int a[10];
int i;
int greatest;
printf("En ter ten values:");
//Store 10 numbers in an array
for (i = 0; i scanf("%d" ,&a[i]);
}
//Assume that a[0] is greatest
greatest = a[0];
for (i = 0; i if (a[i]>greatest){
greatest = a[i];
}
}
printf("\n Greatest of ten numbers is %d", greatest);
return 0;
}
Output:
Enter ten values: 2 53 65 3 88 8 14 5 77 64 Greatest of ten numbers is 88
Explanatio n with example:
Entered values are 2, 53, 65, 3, 88, 8, 14, 5, 77, 64
They are stored in an array of size 10. let a[] be an array holding these values.
/* how the greatest among ten numbers is found */
Let us consider a variable'greatest' . At the beginning of the loop, variable'greatest' is assinged with the value of
first element in the array greatest=a [0]. Here variable'greatest' is assigned 2 as a[0]=2.
Below loop is executed until end of the array'a[]';.
for(i=0; i
{
if(a[i]>gr eatest)
{
greatest= a[i];
}
}
For each value of'i', value of a[i] is compared with value of variable'greatest' . If any value greater than the value
of'greatest' is encountere d, it would be replaced by a[i]. After completion of'for'loop, the value of variable
'greatest' holds the greatest number in the array. In this case 88 is the greatest of all the numbers.
8. Write a program to check whether the given number is a prime.
A prime number is a natural number that has only one and itself as factors. Examples: 2, 3, 13 are prime
numbers.
Program:
#include
main(){
int n, i, c = 0;
printf("En ter any number n: \n");
scanf("%d" ,&n);
/*logic*/
for (i = 1; i
if (n % i == 0){
c++;
}
}
if (c == 2){
printf("n is a Prime number");
}
else{
printf("n is not a Prime number");
}
return 0;
}
Output:
Enter any number n: 7
n is Prime
Explanatio n with examples:
consider a number n=5
for(i=0;i
i.e. for(i=0;i
1st iteration: i=1;i
here i is incremente d i.e. i value for next iteration is 2
now if(n%i==0) then c is incremente d
i.e.if(5%1 ==0)then c is incremente d, here 5%1=0 thus c is incremente d.
now c=1;
2nd iteration: i=2;i
here i is incremente d i.e. i value for next iteration is 3
now if(n%i==0) then c is incremente d
i.e.if(5%2 ==0) then c is incremente d, but 5%2!=0 and so c is not incremente d, c remains 1
c=1;
3rd iteration: i=3;i
here i is incremente d i.e. i value for next iteration is 4
now if(n%i==0) then c is incremente d
i.e.if(5%3 ==0) then c ic incremente d, but 5%3!=0 and so c is not incremente d, c remains 1
c=1;
4th iteration: i=4;i
here i is incremente d i.e. i value for next iteration is 5
now if(n%i==0) then c is incremente d
i.e. if(5%4==0) then c is incremente d, but 5%4!=0 and so c is not incremente d, c remains 1
c=1;
5th iteration: i=5;i
here i is incremente d i.e. i value for next iteration is 6
now if(n%i==0) then c is incremente d
i.e. if(5%5==0) then c is incremente d, 5%5=0 and so c is incremente d.
i.e. c=2
6th iteration: i=6;i
here i value is 6 and 6
now if(c==2) then n is a prime number
we have c=2 from the 5th iteration and thus n=5 is a Prime number.
9. Write a program to check whether the given number is a palindromi c number.
If a number, which when read in both forward and backward way is same, then such a number is called a
palindrome number.
Program:
#include
int main(){
int n, n1, rev = 0, rem;
printf("En ter any number: \n");
scanf("%d" ,&n);
n1 = n;
/* logic */
while (n>0){
rem = n % 10;
rev = rev * 10 + rem;
n = n / 10;
}
if (n1 == rev){
printf("Gi ven number is a palindromi c number");
}
else{
printf("Gi ven number is not a palindromi c number");
}
return 0;
}
Output:
Enter any number: 121
Given number is a palindrome
Explanatio n with an example:
Consider a number n=121, reverse=0, remainder;
number=121
now the while loop is executed /* the condition (n>0) is satisfied */
/* calculate remainder */
remainder of 121 divided by 10=(121%10 )=1;
now reverse=(r everse*10) +remainder
=(0*10)+1 / * we have initialized reverse=0 */
=1
number=num ber/10
=121/10
=12
now the number is 12, greater than 0. The above process is repeated for number=12.
remainder= 12%10=2;
reverse=(1 *10)+2=12;
number=12/ 10=1;
now the number is 1, greater than 0. The above process is repeated for number=1.
remainder= 1%10=1;
reverse=(1 2*10)+1=12 1;
number=1/ 10 / * the condition n>0 is not satisfied,co ntrol leaves the while loop */
Program stops here. The given number=121 equals the reverse of the number. Thus the given number is a
palindrome number.
10.Write a program to check whether the given string is a palindrome .
Palindrome is a string, which when read in both forward and backward way is same.
Example: radar, madam, pop, lol, rubber, etc.,
Program:
#include
#include
int main(){
char string1[20 ];
int i, length;
int flag = 0;
printf("En ter a string: \n");
scanf("%s" , string1);
length = strlen(str ing1);
for(i=0;i<length> if(string1 [i] != string1[le ngth-i-1]) {
flag = 1;
break;
}
}
if (flag){
printf("%s is not a palindrome \n", string1);
}
else{
printf("%s is a palindrome \n", string1);
}
return 0;
}
Output:
Enter a string: radar
"radar"is a palindrome
Explanatio n with example:
To check if a string is a palindrome or not, a string needs to be compared with the reverse of itself.
Consider a palindrome string:"radar",
---------- ---------- -------
index: 0 1 2 3 4
value: r a d a r
---------- ---------- -------
To compare it with the reverse of itself, the following logic is used:
0th character in the char array, string1 is same as 4th character in the same string.
1st character is same as 3rd character.
2nd character is same as 2nd character.
. . . .
ith character is same as'length-i- 1'th character.
If any one of the above condition fails, flag is set to true(1), which implies that the string is not a palindrome .
By default, the value of flag is false(0). Hence, if all the conditions are satisfied, the string is a palindrome .
11.Write a program to generate the Fibonacci series.
Fibonacci series: Any number in the series is obtained by adding the previous two numbers of the series.
Let f(n) be n'th term.
f(0)=0;
f(1)=1;
f(n)=f(n-1 )+f(n-2); (for n>=2)
Series is as follows
011
(1+0)
2 (1+1)
3 (1+2)
5 (2+3)
8 (3+5)
13 (5+8)
21 (8+13)
34 (13+21)
...and so on
Program: to generate Fibonacci Series(10 terms)
#include
int main(){
//array fib stores numbers of fibonacci series
int i, fib[25];
// initialized first element to 0
fib[0] = 0;
// initialized second element to 1
fib[1] = 1;
//loop to generate ten elements
for (i = 2; i //i'th element of series is equal to the sum of i-1'th element and i-2'th element.
fib[i] = fib[i - 1] + fib[i - 2];
}
printf("Th e fibonacci series is as follows \n");
//print all numbers in the series
for (i = 0; i printf("%d \n", fib[i]);
}
return 0;
}
Output:
The fibonacci series is as follows
01123581
3
21
34
Explanatio n:
The first two elements are initialize d to 0, 1 respective ly. Other elements in the series are generated by looping
and adding previous two numbes. These numbers are stored in an array and ten elements of the series are
printed as output.
12.Write a program to print"Hello World"without using semicolon anywhere in the code.
Generally when we use printf("") statement, we have to use a semicolon at the end. If printf is used inside an if
Condition, semicolon can be avoided.
Program: Program to print something without using semicolon (;)
#include
int main(){
//printf returns the length of string being printed
if (printf("H ello World\n")) //prints Hello World and returns 11
{
//do nothing
}
return 0;
}
Output:
Hello World
Explanatio n:
The if statement checks for condition whether the return value of printf("He llo World") is greater than 0. printf
function returns the length of the string printed. Hence the statement if (printf("H ello World")) prints the string
"Hello World".
13.Write a program to print a semicolon without using a semicolon anywhere in the code.
Generally when use printf("") statement we have to use semicolon at the end.
If we want to print a semicolon, we use the statement: printf(";" );
In above statement, we are using two semicolons . The task of printing a semicolon without using semicolon anywhere in the code can be accomplish ed by using the ascii value of';'which is equal to 59.
Program: Program to print a semicolon without using semicolon in the code.
#include
int main(void) {
//prints the character with ascii value 59, i.e., semicolon
if (printf("% c\n", 59)){
//prints semicolon
}
return 0;
}
Output:
;
Explanatio n:
If statement checks whether return value of printf function is greater than zero or not. The return value of function
call printf("%c ",59) is 1. As printf returns the length of the string printed. printf("%c ",59) prints ascii value that
correspond s to 59, that is semicolon( .
14.Write a program to compare two strings without using strcmp() function.
strcmp() function compares two strings lexicograp hically. strcmp is declared in stdio.h
Case 1: when the strings are equal, it returns zero.
Case 2: when the strings are unequal, it returns the difference between ascii values of the characters that differ.
a) When string1 is greater than string2, it returns positive value.
b) When string1 is lesser than string2, it returns negative value.
Syntax:
int strcmp (const char *s1, const char *s2);
Program: to compare two strings.
#include
#include
int cmpstr(cha r s1[10], char s2[10]);
int main(){
char arr1[10] ="Nodalo";
char arr2[10] ="nodalo";
printf("%d", cmpstr(arr 1, arr2));
// cmpstr() is equivalent of strcmp()
return 0;
}/
/s1, s2 are strings to be compared
int cmpstr(cha r s1[10], char s2[10]){
//strlen function returns the length of argument string passed
int i = strlen(s1) ;
int k = strlen(s2) ;
int bigger;
if (i<k> bigger = k;
}
else if (i>k){
bigger = i;
}
else{
bigger = i;
}
//loops'bigger'times
for (i = 0; i<bigger i=""> // if ascii values of characters s1[i], s2[i] are equal do nothing
if (s1[i] == s2[i]){
}
//else return the ascii difference
else{
return (s1[i] - s2[i]);
}
}
//return 0 when both strings are same
//This statement is executed only when both strings are equal
return (0);
}
Output:
-32
Explanatio n:
cmpstr() is a function that illustrate s C standard function strcmp(). Strings to be compared are sent as arguments
to cmpstr().
Each character in string1 is compared to its correspond ing character in string2. Once the loop encounters a
differing character in the strings, it would return the ascii difference of the differing characters and exit.
15.Write a program to concatenat e two strings without using strcat() function.
strcat(str ing1,strin g2) is a C standard function declared in the header file string.h
The strcat() function concatenat es string2, string1 and returns string1.
Program: Program to concatenat e two strings
#include
#include
char *strct(cha r *c1, char *c2);
char *strct(cha r *c1, char *c2){
//strlen function returns length of argument string
int i = strlen(c1) ;
int k = 0;
// loops until null is encountered and appends string c2 to c1
while (c2[k] !='\0'){
c1[i + k] = c2[k];
k++;
}
return c1;
}
int main(){
char string1[15 ] ="first";
char string2[15 ] ="second";
char *finalstr;
printf("Be fore concatenat ion:"
"\n string1 = %s \n string2 = %s", string1, string2);
// addresses of string1, string2 are passed to strct()
finalstr = strcat(str ing1, string2);
printf("\n After concatenat ion:");
//prints the contents of string whose address is in finalstr
printf("\n finalstr = %s", finalstr);
//prints the contents of string1
printf("\n string1 = %s", string1);
//prints the contents of string2
printf("\n string2 = %s", string2);
return 0;
}
Output:
Before concatenat ion:
string1 = first
string2 = second
After concatenat ion:
finalstr = firstsecon d
string1 = firstsecon d
string2 = second
Explanatio n:
string2 is appended at the end of string1 and contents of string2 are unchanged.
In strct() function, using a for loop, all the characters of string'c2'are copied at the end of c1. return (c1) is
equivalent to return&c1[0] and it returns the base address of'c1'.'finalstr' stores that address returned by the
function strct().
16.Write a program to delete a specified line from a text file.
In this program, user is asked for a filename he needs to change. User is also asked for the line number that is
to be deleted. The filename is stored in'filename' . The file is opened and all the data is transferre d to another file
except that one line the user specifies to delete.
Program: Program to delete a specific line.
#include
int main(){
FILE *fp1, *fp2;
// consider 40 character string to store filename
char filename[4 0];
char c;
int del_line, temp = 1;
//asks user for file name
printf("En ter file name:");
// receives file name from user and stores in'filename'
scanf("%s" , filename);
//open file in read mode
fp1 = fopen(file name,"r");
c = getc(fp1);
//until the last character of file is obtained
while (c != EOF)
{
printf("%c ", c);
//print current character and read next character
c = getc(fp1);
}
//rewind
rewind(fp1 );
printf("\n Enter line number of the line to be deleted:") ;
//accept number from user.
scanf("%d" ,&del_line) ;
//open new file in write mode
fp2 = fopen("cop y.c","w");
c = getc(fp1);
while (c != EOF){
c = getc(fp1);
if (c =='\n')
temp++;
//except the line to be deleted
if (temp != del_line)
{
//copy all lines in file copy.c
putc(c, fp2);
}
}
//close both the files.
fclose(fp1 );
fclose(fp2 );
//remove original file
remove(fil ename);
//rename the file copy.c to original name
rename("co py.c", filename);
printf("\n The contents of file after being modified are as follows:\n ");
fp1 = fopen(file name,"r");
c = getc(fp1);
while (c != EOF){
printf("%c ", c);
c = getc(fp1);
}
fclose(fp1 );
return 0;
}
Output:
Enter file name:abc.t xt
hi.
Hello
how are you?
I am fine
hope the same
Enter line number of the line to be deleted:4
The contents of file after being modified are as follows:
hi.
hello
how are you?
hope the same
Explanatio n:
In this program, user is asked for a filename that needs to be modified. Entered file name is stored in a char
array'filename' . This file is opened in read mode using file pointer'fp1'. Character'c'is used to read characters
from the file and print them to the output. User is asked for the line number in the file to be deleted. The file
pointer is rewinded back and all the lines of the file except for the line to be deleted are copied into another file
"copy.c". Now"copy.c"is renamed to the original filename. The original file is opened in read mode and the
modified contents of the file are displayed on the screen.
17.Write a program to replace a specified line in a text file.
Program: Program to replace a specified line in a text file.
#include
int main(void) {
FILE *fp1, *fp2;
// 'filename'i s a 40 character string to store filename
char filename[4 0];
char c;
int del_line, temp = 1;
//asks user for file name
printf("En ter file name:");
// receives file name from user and stores in'filename'
scanf("%s" , filename);
fp1 = fopen(file name,"r");
//open file in read mode
c = getc(fp1);
//print the contents of file .
while (c != EOF){
printf("%c ", c);
c = getc(fp1);
}
//ask user for line number to be deleted.
printf("\n Enter line number to be deleted and replaced") ;
scanf("%d" ,&del_line) ;
//take fp1 to start point.
rewind(fp1 );
//open copy.c in write mode
fp2 = fopen("cop y.c","w");
c = getc(fp1);
while (c != EOF){
if (c =='\n'){
temp++;
}
// till the line to be deleted comes,copy the content from one file to other
if (temp != del_line){
putc(c, fp2);
}
else //when the line to be deleted comes
{
while ((c = getc(fp1)) !='\n'){
}
//read and skip the line ask for new text
printf("En ter new text");
//flush the input stream
fflush(std in);
putc('\n', fp2);
//put'\n'in new file
while ((c = getchar()) !='\n')
putc(c, fp2);
//take the data from user and place it in new file
fputs("\n" , fp2);
temp++;
}
// continue this till EOF is encountere d
c = getc(fp1);
}
//close both files
fclose(fp1 );
fclose(fp2 );
//remove original file
remove(fil ename);
//rename new file with old name opens the file in read mode
rename("co py.c", filename);
fp1 = fopen(file name,"r");
//reads the character from file
c = getc(fp1);
// until last character of file is encountered
while (c != EOF){
printf("%c ", c);
// all characters are printed
c = getc(fp1);
}
//close the file pointer
fclose(fp1 );
return 0;
}
Output:
Enter file name:abc.t xt
hi.
hello
how are you?
hope the same
Enter line number of the line to be deleted and replaced:4
Enter new text: sayonara see you soon
hi.
hello
how are you?
sayonara see you soon
Explanatio n:
In this program, the user is asked to type the name of the file. The File by name entered by user is opened in
read mode. The line number of the line to be replaced is asked as input. Next the data to be replaced is asked. A
new file is opened in write mode named"copy.c". Now the contents of original file are transferre d into new file
and the line to be modified is deleted. New data is stored in its place and remaining lines of the original file are
also transferre d. The copied file with modified contents is replaced with the original file's name. Both the file
pointers are closed and the original file is again opened in read mode and the contents of the original file is
printed as output.
18.Write a program to find the number of lines in a text file.
Number of lines in a file can be determined by counting the number of new line characters present.
Program: Program to count number of lines in a file.
#include
int main()
/* Ask for a filename and count number of lines in the file*/
{
//a pointer to a FILE structure
FILE *fp;
int no_lines = 0;
// consider 40 character string to store filename
char filename[4 0], sample_chr ;
//asks user for file name
printf("En ter file name:");
// receives file name from user and stores in a string named'filename'
scanf("%s" , filename);
//open file in read mode
fp = fopen(file name,"r");
//get character from file and store in sample_chr
sample_chr = getc(fp);
while (sample_ch r != EOF){
// Count whenever sample_chr is'\n'(new line) is encountere d
if (sample_ch r =='\n')
{
// increment variable'no_lines' by 1
no_lines=n o_lines+1;
}
//take next character from file.
sample_chr = getc(fp);
}
fclose(fp) ; //close file.
printf("Th ere are %d lines in %s \n", no_lines, filename);
return 0;
}
Output:
Enter file name:abc.t xt
There are 4 lines in abc.txt
Explanatio n:
In this program, name of the file to be read is taken as input. A file by the given name is opened in read-mode
using a File pointer'fp'. Characters from the file are read into a char variable'sample_ch r'with the help of getc
function. If a new line character( '\n') is encountere d, the integer variable'no_lines' is incremente d. If the
character read into'sample_ch ar'is not a new line character, next character is read from the file. This process is
continued until the last character of the file(EOF) is encountere d. The file pointer is then closed and the total
number of lines is shown as output.
19.Write a C program which asks the user for a number between 1 to 9 and shows the number. If the
user inputs a number out of the specified range, the program should show an error and prompt
the user for a valid input.
Program: Program for accepting a number in a given range.
#include
int getnumber( );
int main(){
int input = 0;
//call a function to input number from key board
input = getnumber( );
//when input is not in the range of 1 to 9,print error message
while (!((input = 1))){
printf("[E RROR] The number you entered is out of range");
//input another number
input = getnumber( );
}
//this function is repeated until a valid input is given by user.
printf("\n The number you entered is %d", input);
return 0;
}/
/this function returns the number given by user
int getnumber( ){
int number;
//asks user for a input in given range
printf("\n Enter a number between 1 to 9 \n");
scanf("%d" ,&number);
return (number);
}
Output:
Enter a number between 1 to 9
45
[ERROR] The number you entered is out of range
Enter a number between 1 to 9
4
The number you entered is 4
Explanatio n:
getfunctio n() function accepts input from user.'while'loop checks whether the number falls within range or not
and accordingl y either prints the number(If the number falls in desired range) or shows error message(nu mber is
out of range).
20.Write a program to display the multiplica tion table of a given number.
Program: Multiplica tion table of a given number
#include
int main(){
int num, i = 1;
printf("\n Enter any Number:");
scanf("%d" ,&num);
printf("Mu ltiplicati on table of %d: \n", num);
while (i
printf("\n %d x %d = %d", num, i, num * i);
i++;
}
return 0;
}
Output:
Enter any Number:5
5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50
Explanatio n:
We need to multiply the given number (i.e. the number for which we want the multiplica tion table)
with value of'i'which increments from 1 to 10.
21. .WAP to check a string is Caliondrom e or not. // Maventic question.
#include
#include
void main()
{
int i,j=0; char a[100];
clrscr();
printf("\n Enter the string to check for caliondrom e:\n");
gets(a);
if(strlen( a)%6)
{
printf("\n %s: is Not a caliondrom e..",a);
getch();
exit(0);
}
for (i=0;a[i]! ='\0'
{
if((a[i]== a[i+5])&&( a[i+1]==a[ i+4])&&(a[ i+2]==a[i+ 3]))
i=i+6;
else
{
j=1;
break;
}
}
if(j)
printf("\n %s: is Not a caliondrom e..",a);
else
printf("\n %s: is a caliondrom e..",a);
getch();
}
22.WAP to print DONE,witho ut using any loop. // asked to my frnd in many company.
#include
void main()
{
static int i=0;
printf("\n %d. DONE",i);
if(i++
main();
getch();
exit(0); / * I used exit(0) to terminate the program after 100 DONE,,i dunno why it was not terminating without using it,may be just at my system,try without it at ur sustem,it sud work */
}
23.WAP to print DONE,witho ut using any loop and any conditonal clause or operators.
/* This code is just in purpose to solve the above question,, but its not a good code in programmin g,as its terminatin g at divide error,,if anyone have a better code,let me know */
main()
{
static int i=100;
printf("%d . DONE\n",10 1-i);
main(1/ --i);
}
/* use"ctrl+f9",then"alt+f5"to see the result */
24. WAP to find out the longest word in a string.
#include
#include
#include
void main()
{
int i,max=0,co unt=0,j;
char str[100]; / * ={"INDIA IS DEMOCRATIC COUNTRY"}; u can use a string inside,in place of user input */
printf("\n Enter the string\n:" );
gets(str);
for(i=0;i
{
if(!(str[i ]==32))
{
count++;
}
else
{
if(max
{
j=i-count;
max=count;
}
count=0;
}
}
for(i=j;i
printf("%c ",str[i]);
getch();
}
25.Prog of WORLD MAP.
#include main(l ,a,n,d)cha r**a;{for(d=atoi (a[1])/ 10*80- atoi(a[2]) / 5-596;n="@N KA\CLCCGZA AQBEAADAFa ISADJABBA^ \SNLGAQABD AXIMBAACTB ATAHDBAN\Z cEMMCCCCAA hEIJFAEAAA BAfHJE\TBd FLDAANEfDN BPHdBcBBBE A_AL\ H E L L O, W O R L D!"[l++-3];)f or(;n-->64 putchar(!d +++33^ l&1);print f("\n\n\n\ n\t\tFound By:\n\t\t\ t Amit Aru");getc h();}
26.WAP to print the triangle of letters in increasing order of lines.
#include
#include
void main()
{
int i,j,k;
char ch;
printf("\n Enter the number of lines wants to make the triangle \n:");
scanf("%d" ,&i);
for(j=1;j
{
ch=65;
for(k=1;k
{
printf("%c ",ch++);
}
printf("\n ");
}
getch();
}
27.WAP to print'xay'in place of every'a'in a string.
#include
#include
void main()
{
int i=0;
char str[100],x ='x',y='y' ;
printf("En ter the string\n:");
gets(str);
while(str[ i]!='\0')
{
if(str[i]= ='a')
{
printf("%c ",x);
printf("%c ",str[i++] );
printf("%c ",y);
}
else
{
printf("%c ",str[i++] );
}
}
getch();
}
28.Count the Total Number of 7 comming between 1 to 100.
/* I made this code in a way that u can give Upper limit i.e. 100,Lower limit i.e. 1 and the specific number u wants to count in between i.e. 7 */
#include
#include
void main()
{
int i,j,U=100, L=1,count= 0,r=1,n;
clrscr();
printf("\n Enter the number u wants to count\n:");
scanf("%d" ,&n);
printf("\n Enter the lower limit\n:");
scanf("%d" ,&L);
printf("\n Enter the upper limit\n:");
scanf("%d" ,&U);
for (i=L;i
{
j=i;
while(j)
{
r=j%10;
if (r==n)
{
count++;
}
j=j/10;
}
}
if(n==0&&L ==0)
count++;
printf("\n Total Number of %d between %d and %d = %d",n,L,U, count);
getch();
}
29. Code for duplicate' s removal,by Amit Aru.
#include
#include
void main()
{
int i,j,k=0,co unt[300]={ 0};
char ch,str[100 0],str1[10 00];
clrscr();
printf("\n Enter the string to remove duplicasy\ n:");
gets(str);
for (i=0;str[i ]!='\0';i+ +)
{
ch=str[i];
count['']=0; / * U can use other delimiter inplace of space''here,just put that char inside'',for ex: count['A']=0 ; if u dnt want any delimiter, just remove this line.*/
if(count[c h])
continue;
else
{
str1[k++]= ch;
count[ch]= 1;
}
}
puts(str1) ;
getch();
}
30. WAP to find out if a given number is a power series of 2 or not,withou t any loop and without using % modulo operator.
#include
#include
int pow2(float );
void main()
{
int i,flag;
clrscr();
printf("En ter the number\n") ;
scanf("%d" ,&i);
flag=pow2( i);
if(flag)
printf("\n %d is power series of 2",i);
else
printf("\n %d is not a power series of 2",i);
getch();
}
int pow2(float j)
{
static float x;
x=j/2;
if(x==2)
return 1;
if(x
return 0;
x=pow2(x);
}
</bigger></k></length>
Tuesday, August 13, 2013
Top 30 Nmap Command Examples For Sys/Network Admins Part 1/3
Top 30 Nmap Command Examples For Sys/Network Admins
Part 1/3
Introduction:
Nmap is short for Network Mapper. It is an open source security tool for network exploration, security scanning and auditing. However, nmap command comes with lots of options that can make the utility more robust and difficult to follow for new users.
The purpose of this post is to introduce a user to the nmap command line tool to scan a host and/or network, so to find out the possible vulnerable points in the hosts. You will also learn how to use Nmap for offensive and defensive purposes.
How to install Nmap - visit www.nmap.org
Let's have a look at the commands!
1: Scan a single host or an IP address (IPv4)
### Scan a single ip address ###
nmap 192.168.1.1
## Scan a host name ###
nmap server1.cyberciti.biz
## Scan a host name with more info###
nmap -v server1.cyberciti.biz
Sample outputs: (see the picture)
2: Scan multiple IP address or subnet (IPv4)
nmap 192.168.1.1 192.168.1.2 192.168.1.3
## works with same subnet i.e. 192.168.1.0/24
nmap 192.168.1.1,2,3
You can scan a range of IP address too:
nmap 192.168.1.1-20
You can scan a range of IP address using a wildcard:
nmap 192.168.1.*
Finally, you scan an entire subnet:
nmap 192.168.1.0/24
3: Read list of hosts/networks from a file (IPv4)
The -iL option allows you to read the list of target systems using a text file. This is useful to scan a large number of hosts/networks. Create a text file as follows:
cat > /tmp/test.txt
Sample outputs:
server1.cyberciti.biz
192.168.1.0/24
192.168.1.1/24
10.1.2.3
localhost
The syntax is:
nmap -iL /tmp/test.txt
4: Excluding hosts/networks (IPv4)
When scanning a large number of hosts/networks you can exclude hosts from a scan:
nmap 192.168.1.0/24 --exclude 192.168.1.5
nmap 192.168.1.0/24 --exclude 192.168.1.5,192.168.1.254
OR exclude list from a file called /tmp/exclude.txt
nmap -iL /tmp/scanlist.txt --excludefile /tmp/exclude.txt
5: Turn on OS and version detection scanning script (IPv4)
nmap -A 192.168.1.254
nmap -v -A 192.168.1.1
nmap -A -iL /tmp/scanlist.txt
6: Find out if a host/network is protected by a firewall
nmap -sA 192.168.1.254
nmap -sA server1.cyberciti.biz
7: Scan a host when protected by the firewall
nmap -PN 192.168.1.1
nmap -PN server1.cyberciti.biz
8: Scan an IPv6 host/address
The -6 option enable IPv6 scanning. The syntax is:
nmap -6 IPv6-Address-Here
nmap -6 server1.cyberciti.biz
nmap -6 2607:f0d0:1002:51::4
nmap -v A -6 2607:f0d0:1002:51::4
9: Scan a network and find out which servers and devices are up and running
This is known as host discovery or ping scan:
nmap -sP 192.168.1.0/24
Sample outputs:
Host 192.168.1.1 is up (0.00035s latency).
MAC Address: BC:AE:C5:C3:16:93 (Unknown)
Host 192.168.1.2 is up (0.0038s latency).
MAC Address: 74:44:01:40:57:FB (Unknown)
Host 192.168.1.5 is up.
Host nas03 (192.168.1.12) is up (0.0091s latency).
MAC Address: 00:11:32:11:15:FC (Synology Incorporated)
Nmap done: 256 IP addresses (4 hosts up) scanned in 2.80 second
10: How do I perform a fast scan?
nmap -F 192.168.1.1
Expect more tomorrow!
Part 1/3
Introduction:
Nmap is short for Network Mapper. It is an open source security tool for network exploration, security scanning and auditing. However, nmap command comes with lots of options that can make the utility more robust and difficult to follow for new users.
The purpose of this post is to introduce a user to the nmap command line tool to scan a host and/or network, so to find out the possible vulnerable points in the hosts. You will also learn how to use Nmap for offensive and defensive purposes.
How to install Nmap - visit www.nmap.org
Let's have a look at the commands!
1: Scan a single host or an IP address (IPv4)
### Scan a single ip address ###
nmap 192.168.1.1
## Scan a host name ###
nmap server1.cyberciti.biz
## Scan a host name with more info###
nmap -v server1.cyberciti.biz
Sample outputs: (see the picture)
2: Scan multiple IP address or subnet (IPv4)
nmap 192.168.1.1 192.168.1.2 192.168.1.3
## works with same subnet i.e. 192.168.1.0/24
nmap 192.168.1.1,2,3
You can scan a range of IP address too:
nmap 192.168.1.1-20
You can scan a range of IP address using a wildcard:
nmap 192.168.1.*
Finally, you scan an entire subnet:
nmap 192.168.1.0/24
3: Read list of hosts/networks from a file (IPv4)
The -iL option allows you to read the list of target systems using a text file. This is useful to scan a large number of hosts/networks. Create a text file as follows:
cat > /tmp/test.txt
Sample outputs:
server1.cyberciti.biz
192.168.1.0/24
192.168.1.1/24
10.1.2.3
localhost
The syntax is:
nmap -iL /tmp/test.txt
4: Excluding hosts/networks (IPv4)
When scanning a large number of hosts/networks you can exclude hosts from a scan:
nmap 192.168.1.0/24 --exclude 192.168.1.5
nmap 192.168.1.0/24 --exclude 192.168.1.5,192.168.1.254
OR exclude list from a file called /tmp/exclude.txt
nmap -iL /tmp/scanlist.txt --excludefile /tmp/exclude.txt
5: Turn on OS and version detection scanning script (IPv4)
nmap -A 192.168.1.254
nmap -v -A 192.168.1.1
nmap -A -iL /tmp/scanlist.txt
6: Find out if a host/network is protected by a firewall
nmap -sA 192.168.1.254
nmap -sA server1.cyberciti.biz
7: Scan a host when protected by the firewall
nmap -PN 192.168.1.1
nmap -PN server1.cyberciti.biz
8: Scan an IPv6 host/address
The -6 option enable IPv6 scanning. The syntax is:
nmap -6 IPv6-Address-Here
nmap -6 server1.cyberciti.biz
nmap -6 2607:f0d0:1002:51::4
nmap -v A -6 2607:f0d0:1002:51::4
9: Scan a network and find out which servers and devices are up and running
This is known as host discovery or ping scan:
nmap -sP 192.168.1.0/24
Sample outputs:
Host 192.168.1.1 is up (0.00035s latency).
MAC Address: BC:AE:C5:C3:16:93 (Unknown)
Host 192.168.1.2 is up (0.0038s latency).
MAC Address: 74:44:01:40:57:FB (Unknown)
Host 192.168.1.5 is up.
Host nas03 (192.168.1.12) is up (0.0091s latency).
MAC Address: 00:11:32:11:15:FC (Synology Incorporated)
Nmap done: 256 IP addresses (4 hosts up) scanned in 2.80 second
10: How do I perform a fast scan?
nmap -F 192.168.1.1
Expect more tomorrow!
Thursday, August 1, 2013
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