How to print all the Armstrong Numbers from 1 to 1000 using C#?

An Armstrong number (also called a narcissistic number) is a number that equals the sum of its own digits raised to the power of the number of digits. For 3-digit numbers, each digit is cubed and summed. For example, 153 is an Armstrong number because 1³ + 5³ + 3³ = 1 + 125 + 27 = 153.

To find all Armstrong numbers from 1 to 1000, we need to check each number by extracting its digits, calculating the sum of cubes, and comparing it with the original number.

Algorithm

The steps to identify Armstrong numbers are −

• Extract each digit of the number

• Calculate the cube of each digit

• Sum all the cubes

• Compare the sum with the original number

Extracting Digits

For a 3-digit number, we can extract individual digits using modulo and division operations −

d1 = val % 10;              // units digit
d2 = (val / 10) % 10;       // tens digit  
d3 = (val / 100) % 10;      // hundreds digit

Complete Program

using System;

class Program {
   public static void Main() {
      Console.WriteLine("Armstrong numbers from 1 to 1000:");
      int val = 1;
      
      while (val <= 1000) {
         int d1, d2, d3, res;
         
         // Extract digits
         d1 = val % 10;              // units digit
         d2 = (val / 10) % 10;       // tens digit
         d3 = (val / 100) % 10;      // hundreds digit
         
         // Calculate sum of cubes
         res = (d1 * d1 * d1) + (d2 * d2 * d2) + (d3 * d3 * d3);
         
         // Check if Armstrong number
         if (res == val) {
            Console.WriteLine(val);
         }
         
         val++;
      }
   }
}

The output of the above code is −

Armstrong numbers from 1 to 1000:
1
153
371
407

Using a More General Approach

For a more flexible solution that works with numbers of any length, we can use a method that dynamically calculates the number of digits −

using System;

class Program {
   public static bool IsArmstrong(int number) {
      int original = number;
      int sum = 0;
      int digits = number.ToString().Length;
      
      while (number > 0) {
         int digit = number % 10;
         sum += (int)Math.Pow(digit, digits);
         number /= 10;
      }
      
      return sum == original;
   }
   
   public static void Main() {
      Console.WriteLine("Armstrong numbers from 1 to 1000:");
      
      for (int i = 1; i <= 1000; i++) {
         if (IsArmstrong(i)) {
            Console.WriteLine(i);
         }
      }
   }
}

The output of the above code is −

Armstrong numbers from 1 to 1000:
1
2
3
4
5
6
7
8
9
153
371
407

Conclusion

Armstrong numbers are found by checking if a number equals the sum of its digits raised to the power of the digit count. In the range 1 to 1000, the Armstrong numbers are: 1, 2, 3, 4, 5, 6, 7, 8, 9, 153, 371, and 407. The general approach using Math.Pow() works for numbers of any length.