Here is a program to find whether the entered number is a prime or not. A prime number is a one, whose divisors are 1 and the number itself.

**Logic: **The program expects the user to enter the number to check for prime property. The for loop in the program traces the iteration till the number, while in each of iteration it checks the present number is the divisor of the entered or not. If it is, it sets the flag to 1 and breaks off, which effectively prints out the result through the if block.

The same algorithm is modified slightly, and developed a program to print all the prime number till the user defined range.

Program to find whether a number is a prime or not

#include<stdio.h>

void main()

{

int i, prime = 1, n;

clrscr();

printf(“\n\n\t ENTER A NUMBER…: “);

scanf(“%d”, &n);

for(i=2; i<n; i++)

{

if(n%i == 0)

{

prime = 0;

break;

}

}

if(prime)

printf(“\n\n\t THE NUMBER %d IS A PRIME NUMBER”, n);

else

printf(“\n\n\t THE NUMBER %d IS NOT A PRIME NUMBER”, n);

getch();

}

very helpful