I have used Visual Studio 2012 for debugging purpose. But you can use any version of visul studio as per your availability.

What is Armstrong number?

An Armstrong number is an n-digit number that is equal to the sum of the nth powers of its digits.

For Example: 407 = 43 + 03 + 73 = 64 + 0 + 343 = 407

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
public class csharpExercise
{
    static void Main(string[] args)
    {
        int lower, higher, i, temp1, temp2, remainder, n = 0;
        double result = 0;
 
        // Reading number
        Console.Write("Please Enter two numbers: ");
        lower = Convert.ToInt32(Console.ReadLine());
        higher = Convert.ToInt32(Console.ReadLine());
 
        Console.Write("Armstrong numbers between " + lower + " and " +  higher + " are: ");
 
        for (i = lower + 1; i < higher; ++i)
        {
            temp2 = i;
            temp1 = i;
 
            // number of digits calculation
            while (temp1 != 0)
            {
                temp1 /= 10;
                ++n;
            }
 
            // result contains sum of nth power of its digits
            while (temp2 != 0)
            {
                remainder = temp2 % 10;
                result += Math.Pow(remainder, n);
                temp2 /= 10;
            }
 
            // checking if number i is equal to the sum of nth power of its digits
            if (result == i)
            {
               Console.WriteLine(i);
            }
 
            // resetting the values to check Armstrong number for next iteration
            n = 0;
            result = 0;
 
        }
 
        Console.ReadLine();
    }
}

Result:

Please Enter two numbers: 200

500

Armstrong numbers between 200 and 500 are: 370

371

407