C Program to check if a input number is a prime number or not

Published on December 18, 2016 by abundantcode

Filed under C

Last modified December 18, 2016

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Problem

Write a program in C to check whether a number is a prime number or not.

How to find if a number is a prime number in C ?

A Prime Number is a number that is divisible by 1 and by itself. Some of the examples of the prime number are 2 , 3 , 5 etc.

Here’s a program in C demonstrating how to find whether the given number is a prime number or not.

#include <stdio.h>
int main()
{
    int input, index;
    int flag=0;
    printf("Abundantcode.com coding sample \n");
    
    printf("Enter a number : ");
    scanf("%d",&input);

    for(index=2; index<=input/2; ++index)
    {
        if(input%index==0)
        {
            flag=1;
            break;
        }
    }

    if (flag==0)
        printf("%d is a prime number.",input);
    else
        printf("%d is not a prime number.",input);
    
    return 0;
}

Output

Abundantcode.com coding sample                                            
Enter a number : 7

7 is a prime number.

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