C program to check a given number is prime or not using recursion

Here, we will read an integer number from the user and then check the given number is a prime number or not using a recursive function.

Program:

The source code to check a given number is prime or not using recursion is given below. The given program is compiled and executed using GCC compile on UBUNTU 18.04 OS successfully.

// C program to check a given number is prime or not 
// using recursion

#include <stdio.h>

int checkPrime(int num, int i)
{
    if (i != 1) {
        if (num % i != 0) {
            return checkPrime(num, i - 1);
        }
        else {
            return 0;
        }
    }
    else {
        return 1;
    }
}

int main()
{
    int num = 0;

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

    if (checkPrime(num, num / 2) == 1)
        printf("Given number is prime number");
    else
        printf("Given number is not prime number");

    return 0;
}

Output:

RUN 1:
Enter a number: 113
Given number is prime number

RUN 2:
Enter a number: 71
Given number is prime number

RUN 3:
Enter a number: 108
Given number is not prime number

RUN 4:
Enter a number: 21
Given number is not prime number

Explanation:

In the above program, we created two functions checkPrime() and main() function. The checkPrime() function is a recursive function, which is used to check a given number is a prime number or not.

In the main() function, we read an integer number from the user and then check the given number is a prime number or not using the checkPrime() function and printed the result on the console screen.