A prime number is a positive integer which is divisible only by 1 and itself. For example: 2, 3, 5, 7, 11, 13

## Example: Program to Check Prime Number

```
#include <stdio.h>
int main()
{
int n, i, flag = 0;
printf("Enter a positive integer: ");
scanf("%d",&n);
for(i=2; i<=n/2; ++i)
{
// condition for nonprime number
if(n%i==0)
{
flag=1;
break;
}
}
if (flag==0)
printf("%d is a prime number.",n);
else
printf("%d is not a prime number.",n);
return 0;
}
```

**Output**

`Enter a positive integer: 29
29 is a prime number.`

If the `for`

loop terminates when the test expression of loop `i <= n/2`

is false, the entered number is a prime number. The value of `flag` is equal to 0 in this case.

If the loop terminates because of `break`

statement inside the `if`

statement, the entered number is a nonprime number. The value of flag is 1 in this case.

Visit this page to learn, how you can display all prime numbers between two intervals entered by the user.