By | 29.11.2016

# C Program to Find Number is Prime or Not

Write a C Program to Find Number is Prime or Not using Recursion. Here’s simple Program to Find Number is Prime or Not using Recursion in C Programming Language.

## Recursion : :

• Recursion is the process of repeating items in a self-similar way. In programming languages, if a program allows you to call a function inside the same function, then it is called a recursive call of the function.
• The C programming language supports recursion, i.e., a function to call itself. But while using recursion, programmers need to be careful to define an exit condition from the function, otherwise it will go into an infinite loop.
• Recursive functions are very useful to solve many mathematical problems, such as calculating the factorial of a number, generating Fibonacci series, etc.

## Problem : :

The following C program, using recursion, finds whether the entered number is prime number or not. A prime number is an integer that has no integral factor but itself and 1.

Below is the source code for C Program to Find Number is Prime or Not using Recursion which is successfully compiled and run on Windows System to produce desired output as shown below :

### SOURCE CODE : :

```/* C Program to Find Number is Prime or Not using Recursion */

#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);
}
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);
}
}
}```

### Output : :

```***************** OUTPUT ****************

***************** FIRST RUN *****************

Enter a number: 675
675 is not a prime number

***************** SECOND RUN *****************

Enter a number: 467
467 is a prime number```

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