A prime number can be divided by 1 and itself, there are no other divisors,

Examples are : 2 3, 5, 7, 11, …..

To find out whether a given number is prime or not, here is the logic

1. Get the number

2. divide the given number from 2 to n-1 (Example if 6 is the number divided by 2,3,4,5 will get the remainder respectively 0,0,2,3)

3. increment a counter to 1 if the remainder is 0

4. if there counter variable is 0, then the given number is prime (because we didn’t get any remainder) else non prime

Here is the program

#include <stdio.h>

#include <conio.h>int main()

{

int a,i,count=0;

printf("enter a");//Let the given number is a

scanf("%d",&a);//get the numberfor(i=2;i<a;i++)//divide the number a from 2 to a-1

{

if(a%i==0)

count++;//increment a counter if the divisibility is 0}

if(count !=0)//if the counter is not zero, then prime

printf("a is not a prime number");

else

printf("a is a prime number");

getch();

return 0;

}