Prime Number program in C

Sure! Here’s an example of a program in C that checks whether a given number is prime or not:

#include <stdio.h>

int isPrime(int num) {
    if (num <= 1) {
        return 0;  // not a prime number

    for (int i = 2; i * i <= num; i++) {
        if (num % i == 0) {
            return 0;  // not a prime number

    return 1;  // prime number

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);

    if (isPrime(num)) {
        printf("%d is a prime number.\n", num);
    } else {
        printf("%d is not a prime number.\n", num);

    return 0;

In this program, the isPrime function takes an integer as input and checks whether it is prime or not. It follows the basic primality test algorithm, where it iterates from 2 to the square root of the number and checks if any number divides the given number. If a divisor is found, the number is not prime.

In the main function, the user is prompted to enter a number, which is then passed to the isPrime function. Based on the return value, the program displays whether the number is prime or not.

Note: This program assumes that the input number is an integer greater than or equal to zero.