Example: Check Prime or Armstrong Number in C

// Check Prime or Armstrong Number
#include <stdio.h>
#include <math.h> // Required for sqrt() and pow()

// Function to check if a number is prime (from Approach 1)
int isPrime(int num) {
    if (num <= 1) {
        return 0;
    }
    for (int i = 2; i <= sqrt(num); i++) {
        if (num % i == 0) {
            return 0;
        }
    }
    return 1;
}

// Function to check if a number is an Armstrong number (from Approach 2)
int isArmstrong(int num) {
    int originalNum, remainder, n = 0;
    double result = 0.0;

    originalNum = num;

    int tempNum = num;
    if (num == 0) { // Handle 0 separately for digit count
        n = 1;
    } else {
        while (tempNum != 0) {
            tempNum /= 10;
            n++;
        }
    }

    tempNum = num; // Reset tempNum for sum of powers calculation
    while (tempNum != 0) {
        remainder = tempNum % 10;
        result += pow(remainder, n);
        tempNum /= 10;
    }

    if ((int)result == originalNum) {
        return 1;
    } else {
        return 0;
    }
}

int main() {
    int number;

    // Step 1: Prompt user for input
    printf("Enter a positive integer: ");
    scanf("%d", &number);

    // Step 2: Check if the number is prime using the isPrime function
    if (isPrime(number)) {
        printf("%d is a Prime number.\n", number);
    } else {
        printf("%d is not a Prime number.\n", number);
    }

    // Step 3: Check if the number is an Armstrong number using the isArmstrong function
    if (isArmstrong(number)) {
        printf("%d is an Armstrong number.\n", number);
    } else {
        printf("%d is not an Armstrong number.\n", number);
    }

    return 0;
}