C Program for Armstrong Numbers

An Armstrong number (also known as narcissistic number) is a number that is equal to the sum of its own digits raised to the power of the number of digits. For example, 153 is an Armstrong number because 1³ + 5³ + 3³ = 1 + 125 + 27 = 153.

Syntax

int armstrong(int number);

Formula

For an n-digit number with digits d?, d?, ..., d? ?

Armstrong Number = d?? + d?? + ... + d??

Example

This program checks if a given number is an Armstrong number using helper functions to calculate power and count digits ?

#include <stdio.h>

int power(int a, int b) {
    int result = 1;
    while (b > 0) {
        result *= a;
        b--;
    }
    return result;
}

int countDigits(int n) {
    int count = 0;
    while (n != 0) {
        count++;
        n = n / 10;
    }
    return count;
}

int armstrong(int n) {
    int original = n;
    int digits = countDigits(n);
    int sum = 0;
    
    while (n > 0) {
        int digit = n % 10;
        sum += power(digit, digits);
        n /= 10;
    }
    return sum;
}

int main() {
    int number = 1634;
    
    if (number == armstrong(number)) {
        printf("%d is an Armstrong number<br>", number);
    } else {
        printf("%d is not an Armstrong number<br>", number);
    }
    
    // Test with more examples
    int testNumbers[] = {153, 371, 9474, 123};
    int size = sizeof(testNumbers) / sizeof(testNumbers[0]);
    
    printf("\nTesting other numbers:<br>");
    for (int i = 0; i < size; i++) {
        if (testNumbers[i] == armstrong(testNumbers[i])) {
            printf("%d is an Armstrong number<br>", testNumbers[i]);
        } else {
            printf("%d is not an Armstrong number<br>", testNumbers[i]);
        }
    }
    
    return 0;
}

1634 is an Armstrong number

Testing other numbers:
153 is an Armstrong number
371 is an Armstrong number
9474 is an Armstrong number
123 is not an Armstrong number

How It Works

1. countDigits() ? Counts the total number of digits in the given number
2. power() ? Calculates the power of a digit raised to the number of digits
3. armstrong() ? Extracts each digit, raises it to the power of total digits, and sums them up
4. main() ? Compares the original number with the calculated sum

Common Armstrong Numbers

Conclusion

Armstrong numbers are special mathematical numbers where the sum of digits raised to the power of digit count equals the original number. This C program efficiently checks Armstrong numbers using modular functions for better code organization.