C Program to Find wher a Number is Prime or Not using Recursion

This is a C program to find whether a number is prime or not using recursion.

Problem Description

The following C program, using recursion, finds whether the entered number is a prime number or not.

Problem Solution

A prime number is an integer that has no integral factor but itself and 1.

Program/Source Code

#include <stdio.h>
 
int primeno(int, int);
 
int main()
{
    int num, check;
    printf("Enter a number: ");
    scanf("%d", &num);
    check = primeno(num, num / 2);
    if (check == 1)
    {
        printf("%d is a prime number\n", num);
    }
 &nb....Show More

This is a C program to find whether a number is prime or not using recursion.

Problem Description

The following C program, using recursion, finds whether the entered number is a prime number or not.

Problem Solution

A prime number is an integer that has no integral factor but itself and 1.

Program/Source Code

#include 
 
int primeno(int, int);
 
int main()
{
    int num, check;
    printf("Enter a number: ");
    scanf("%d", &num);
    check = primeno(num, num / 2);
    if (check == 1)
    {
        printf("%d is a prime number\n", num);
    }
    else
    {
        printf("%d is not a prime number\n", num);
    }
    return 0;
}
 
int primeno(int num, int i)
{
    if (i == 1)
    {
        return 1;
    }
    else
    {
       if (num % i == 0)
       {
         return 0;
       }
       else
       {
         return primeno(num, i - 1);
       }       
    }
}

Program Explanation

In this C program, we are reading the integer number using num variable. A prime number is an integer that has no integral factor but itself and 1. The check variable is used to call the primeno() function by passing the value of num variable and the value of division of num variable value by 2 as an argument.

The primeno() function is used to find whether the entered number is a prime number or not. If else condition statement is used to check the value of i variable is equal to 1 and return the value of i variable to the called variable check.

Otherwise, if the condition is false execute the else statement and call the primeno() function by passing the value of num variable and the decrement the value of i variable by 1. Return the resulted value to the called variable check.

If else condition statement is used to check that the value of check variable is equal to 1. If the condition is true print the statement as prime number. Otherwise, if the condition is false print the statement as not a prime number.

Output:

Enter a number: 456

456 is not a prime number

 

Enter a number: 89

89 is a prime number