Q:

How to find whether a given number is prime number in C?

belongs to collection: C Programming on Numbers

YasminRadwan26
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2022-06-19
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In this exercise, I will discuss only the trial division method for another algorithm

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YasminRadwan26
2022-06-19
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In the below code to check prime number, we are checking that the given number n is a multiple of any integer between 2 and (n -1) or not. If the given number n is a multiple of any integer between 2 and (n -1), then n will be not a prime number.

#include <stdio.h>
#define PRIME_NUMBER  1
int isPrimeNumber(int number)
{
    int iLoop = 0;
    int iPrimeFlag = 1;
    //check for negative number and one
    if(number <= 1)
    {
        iPrimeFlag = 0;
    }
    else
    {
        for(iLoop = 2; iLoop < number; iLoop++)
        {
            // check prime number
            if((number % iLoop) == 0)
            {
                //update the flag when number is not prime
                iPrimeFlag = 0;
                break;
            }
        }
    }
    return iPrimeFlag;
}
int main()
{
    int iRetValue = 0;
    int number = 0;
    printf("Enter the number : ");
    scanf("%d",&number);
    iRetValue = isPrimeNumber(number);
    //Check for prime number
    if (iRetValue == PRIME_NUMBER)
    {
        printf("\n\n%d is prime number..\n\n", number);
    }
    else
    {
        printf("\n\n%d is not a prime number..\n\n", number);
    }
    return 0;
}

Output:

Enter the number : 2

2 is prime number..

-----------------------------

Enter the number : 10

10 is not a prime number..

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