The Program in C# Program to check If Given number is Armstrong number or not is given below:

using System;

namespace ArmstrongNumber
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello Codeauri Family, enter the number to check for Armstrong number:");
            int number = int.Parse(Console.ReadLine());

            int originalNumber = number;
            int result = 0;
            int digits = 0;

            while (originalNumber != 0)
            {
                originalNumber /= 10;
                digits++;
            }

            originalNumber = number;

            while (originalNumber != 0)
            {
                int remainder = originalNumber % 10;
                result += (int) Math.Pow(remainder, digits);
                originalNumber /= 10;
            }

            if (result == number)
            {
                Console.WriteLine(number + " is an Armstrong number.");
            }
            else
            {
                Console.WriteLine(number + " is not an Armstrong number.");
            }

            Console.ReadLine();
        }
    }
}

Output:

Hello Codeauri Family, enter the number to check for Armstrong number:
371
371 is an Armstrong number.

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Here are the step by step execution of above program:

1. The Main method starts by asking the user to enter a number to check for Armstrong number.
2. The input is stored in the number variable and the originalNumber variable is initialized with the same value.
3. The number of digits in the input number is calculated by dividing the originalNumber by 10 until it becomes 0 and counting the number of divisions. This value is stored in the digits variable.
4. The originalNumber is then used in a while loop to calculate the sum of each digit raised to the power of digits.
5. If the result is equal to the input number, the number is considered an Armstrong number and the message “is an Armstrong number” is displayed.
6. If the result is not equal to the input number, the number is not considered an Armstrong number and the message “is not an Armstrong number” is displayed.
7. The program pauses at the end to wait for the user’s input before exiting.