C Program to Check Prime or Armstrong Number Using User-defined Function

In this program, two user-defined functions checkPrimeNumber() and checkArmstrongNumber() are created.


The checkPrimeNumber() returns 1 if the number entered by the user is a prime number. Similarly, checkArmstrongNumber() returns 1 if the number entered by the user is an Armstrong number.

#include  < stdio.h >
#include  < math.h >

int checkPrimeNumber(int n);
int checkArmstrongNumber(int n);

int main()
{
    int m, flag;

    printf("Enter a positive integer: ");
    scanf("%d", &m);

    // Check prime number
    flag = checkPrimeNumber(m);
    if (flag == 1)
        printf("%d is a prime number.\n", m);
    else
        printf("%d is not a prime number.\n", m);

    // Check Armstrong number
    flag = checkArmstrongNumber(m);
    if (flag == 1)
        printf("%d is an Armstrong number.", m);
    else
        printf("%d is not an Armstrong number.",m);
    return 0;
}

int checkPrimeNumber(int m)
{
    int i, flag = 1;

    for(i=2; i < =m/2; ++i)
    {

    // condition for non-prime number
        if(m%i == 0)
        {
            flag = 0;
            break;
        }
    }
    return flag;
}

int checkArmstrongNumber(int number)
{
    int originalNumber, remainder, result = 0, m = 0, flag;

    originalNumber = number;

    while (originalNumber != 0)
    {
        originalNumber /= 10;
        ++m;
    }

    originalNumber = number;

    while (originalNumber != 0)
    {
        remainder = originalNumber%10;
        result += pow(remainder, m);
        originalNumber /= 10;
    }

    // condition for Armstrong number
    if(result == number)
        flag = 1;
    else
        flag = 0;

    return flag;
}
Output

Enter a positive integer: 407
407 is not a prime number.
407 is an Armstrong number.