## Q. C program to Check Whether a Number is Prime or not.

Here you will find an algorithm and program in C programming language to check whether the given number is prime number or not. First let us understand what prime number means.

**Explanation : **A number that is divisible by only and only 1 and itself is known as a Prime Number. For example: - 11 is only divisible by 1, so 11 is prime, while 10 is divisible by 1, 2, and 5 so 10 is not a prime number.

## Prime Number Algorithm

START Step 1 → Take integer variable A Step 2 → Divide the variable A with (A/2 to 2) Step 3 → If A is divisible by any value (A/2 to 2) then it is not prime Step 4 → Else it is prime number STOP

# C Program to Check Whether a Number is Prime or Not

#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) { if (n % i == 0) { flag = 1; break; } } if (n == 1) { printf("1 is neither prime nor composite."); } else { if (flag == 0) printf("This is a prime number."); else printf("This is not a prime number."); } return 0; }

#### Output

Enter a positive integer : 17 This is a prime number. Enter a positive integer : 25 This is not a prime number.