Write a Program in C to Determine Whether a Number is Prime or Not.

"A prime number is one, which is divisible only by 1 or itself."

To determine whether a number is prime or not, we have to divide the number successively by all numbers from 2 to one less than itself.

If remainder of any of these divisions is zero, the number is not a prime.

If no division yields a zero then the number is a prime number.

Program in C to Determine Whether a Number is Prime or Not

Steps:

Declare integers num and i inside main()
Prompt the message allow the input using printf() and scanf()
Test whether a Number is prime or not using while() function.

Code:

#include <stdio.h>

int main()
 {

 int num, i;     


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

 i=2;

 while (i<=num-1)
 {

 if (num%i==0)
 {
  printf("Not a prime number\n");
  break;
 }

 i++;
 }

 if (i==num)

 printf("Prime number\n");

 return 0;
 }