C# Program to Check Whether the Entered Number is an Armstrong Number or Not

An Armstrong number (also called a narcissistic number) is a number that equals the sum of its digits raised to the power of the number of digits. For a 3-digit number, each digit is cubed and summed.

For example, 153 is an Armstrong number because −

1³ + 5³ + 3³ = 1 + 125 + 27 = 153

Algorithm

The algorithm to check an Armstrong number involves these steps −

• Extract each digit from the number using modulo operation

• Calculate the cube of each digit and add to the sum

• Compare the final sum with the original number

Following is the core logic to extract digits and calculate sum −

for (int i = val; i > 0; i = i / 10) {
    rem = i % 10;
    sum = sum + rem * rem * rem;
}

Example

Here is a complete program to check if a number is an Armstrong number −

using System;

class Program {
    static void Main(string[] args) {
        int val = 153, sum = 0;
        int rem;
        int original = val;

        // Extract digits and calculate sum of cubes
        for (int i = val; i > 0; i = i / 10) {
            rem = i % 10;
            sum = sum + rem * rem * rem;
        }

        // Check if sum equals original number
        if (sum == original) {
            Console.WriteLine(original + " is an Armstrong Number");
        } else {
            Console.WriteLine(original + " is not an Armstrong Number");
        }
    }
}

The output of the above code is −

153 is an Armstrong Number

Testing Multiple Numbers

Here's an example that checks multiple numbers to demonstrate both Armstrong and non-Armstrong numbers −

using System;

class Program {
    static bool IsArmstrong(int num) {
        int sum = 0, original = num, rem;
        
        while (num > 0) {
            rem = num % 10;
            sum = sum + rem * rem * rem;
            num = num / 10;
        }
        
        return sum == original;
    }
    
    static void Main(string[] args) {
        int[] numbers = {153, 371, 407, 123, 456};
        
        foreach (int number in numbers) {
            if (IsArmstrong(number)) {
                Console.WriteLine(number + " is an Armstrong Number");
            } else {
                Console.WriteLine(number + " is not an Armstrong Number");
            }
        }
    }
}

The output of the above code is −

153 is an Armstrong Number
371 is an Armstrong Number
407 is an Armstrong Number
123 is not an Armstrong Number
456 is not an Armstrong Number

Conclusion

An Armstrong number equals the sum of its digits raised to the power of the number of digits. The algorithm involves extracting each digit, cubing it, summing all cubes, and comparing with the original number to determine if it's an Armstrong number.