# C program to check whether a number is prime or not

## What is prime number ?

A prime number is a natural number that is divisible by 1 and itself only.

For example 2, 3, 5, 7….

Please go through following articles of C programming to understand the logic of the program.

# C program to check prime number

``````#include <stdio.h>

int main()
{
int num, i, j = 0;

printf("Enter number: ");
scanf("%d", &num);

//check for prime number
for (i = 1; i <= num; i++)
{
if ((num % i) == 0)
{
j++;
}
}

if (j == 2)
printf("%d is a prime number.", num);
else
printf("%d is not a prime number.", num);

return 0;
}
``````

Output Explanation

Program logic of the above program to check whether a number is prime or not is simple. We know that prime number is only divisible by 1 and itself.

Hence every time the program flow enters `for` loop it checks whether the number is divisible by iteration number.

If the given number is perfectly divided by iteration number then `j` is increased by `1`. This continues till iteration reached to number itself.

Finally, the value of `j` is checked and if it is equal to 2, the result is a prime number.