Check whether a given number is an Armstrong Number

Step 1: Design Page – ArmstrongNumber.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="ArmstrongNumber.aspx.cs" Inherits="ArmstrongNumber" %>

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Armstrong Number Checker - Real Time Example</title>
    <style>
        body {
            font-family: Arial;
            background-color: #f0f2f5;
            margin: 50px;
        }
        .container {
            width: 420px;
            margin: auto;
            background: white;
            border-radius: 8px;
            box-shadow: 0px 0px 10px #ccc;
            padding: 20px;
        }
        h2 {
            color: #1A2A80;
            text-align: center;
        }
        .form-control {
            width: 100%;
            padding: 8px;
            margin-top: 10px;
        }
        .btn {
            background-color: #7A85C1;
            color: white;
            border: none;
            padding: 10px 20px;
            margin-top: 10px;
            border-radius: 5px;
            cursor: pointer;
        }
        .result {
            font-weight: bold;
            color: #333;
            margin-top: 15px;
            text-align: center;
        }
    </style>
</head>
<body>
    <form id="form1" runat="server">
        <div class="container">
            <h2>Armstrong Number Checker</h2>

            <asp:Label ID="lblNumber" runat="server" Text="Enter a Number:"></asp:Label><br />
            <asp:TextBox ID="txtNumber" runat="server" CssClass="form-control" placeholder="Example: 153"></asp:TextBox><br />

            <asp:Button ID="btnCheck" runat="server" Text="Check Armstrong" CssClass="btn" OnClick="btnCheck_Click" /><br />

            <asp:Label ID="lblResult" runat="server" CssClass="result"></asp:Label>
        </div>
    </form>
</body>
</html>

Step 2: Backend Logic – ArmstrongNumber.aspx.cs

using System;

public partial class ArmstrongNumber : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }

    protected void btnCheck_Click(object sender, EventArgs e)
    {
        int number;
        bool isValid = int.TryParse(txtNumber.Text.Trim(), out number);

        if (!isValid || number < 0)
        {
            lblResult.Text = "Please enter a valid positive number.";
            lblResult.ForeColor = System.Drawing.Color.Red;
            return;
        }

        if (IsArmstrong(number))
        {
            lblResult.Text = $"{number} is an Armstrong Number.";
            lblResult.ForeColor = System.Drawing.Color.Green;
        }
        else
        {
            lblResult.Text = $"{number} is NOT an Armstrong Number.";
            lblResult.ForeColor = System.Drawing.Color.Red;
        }
    }

    private bool IsArmstrong(int num)
    {
        int original = num;
        int sum = 0;
        int digits = num.ToString().Length;  // Count number of digits

        while (num > 0)
        {
            int digit = num % 10;
            sum += (int)Math.Pow(digit, digits);  // Add power of each digit
            num /= 10;
        }

        return sum == original;
    }
}

Real-Time Example Flow

Open ArmstrongNumber.aspx in your browser.
Enter 153 and click “Check Armstrong”.
The result displays:

“153 is an Armstrong Number.”
If you enter 123, output:

“123 is NOT an Armstrong Number.”

Explanation

Step	Description
1	Take the input number from the user.
2	Count total digits.
3	Separate each digit using modulus %.
4	Raise each digit to the power of total digits and add them.
5	Compare the sum with the original number.
6	If equal → Armstrong number, else not.

Sample Input / Output

Input	Calculation	Result
153	1³ + 5³ + 3³ = 153	Armstrong
370	3³ + 7³ + 0³ = 370	Armstrong
371	3³ + 7³ + 1³ = 371	Armstrong
9474	9⁴ + 4⁴ + 7⁴ + 4⁴ = 9474	Armstrong
123	1³ + 2³ + 3³ = 36	Not Armstrong