Find the sum of digits of a number

Step 1: Design Page – SumOfDigits.aspx

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

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Sum of Digits - Real Time Example</title>
    <style>
        body {
            font-family: Arial;
            background-color: #f0f2f5;
            margin: 50px;
        }
        .container {
            width: 400px;
            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>Sum of Digits of a Number</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: 1234"></asp:TextBox><br />

            <asp:Button ID="btnFindSum" runat="server" Text="Find Sum of Digits" CssClass="btn" OnClick="btnFindSum_Click" /><br />

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

Step 2: Backend Logic – SumOfDigits.aspx.cs

using System;

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

    protected void btnFindSum_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;
        }

        int sum = FindSumOfDigits(number);
        lblResult.Text = $"The sum of digits of {number} is {sum}.";
        lblResult.ForeColor = System.Drawing.Color.Green;
    }

    private int FindSumOfDigits(int num)
    {
        int sum = 0;
        while (num > 0)
        {
            sum += num % 10;  // Get the last digit
            num /= 10;        // Remove the last digit
        }
        return sum;
    }
}

Real-Time Example Flow

Run the page SumOfDigits.aspx.
Enter a number like 1234.
Click “Find Sum of Digits”.
The result displays:

✅“The sum of digits of 1234 is 10.”

Explanation

Component	Purpose
TextBox (txtNumber)	To input the number.
Button (btnFindSum)	Executes the logic on click.
FindSumOfDigits()	Uses % and / operators to extract and sum digits.
Label (lblResult)	Displays result dynamically.

Sample Input / Output

Input	Output
123	6
987	24
5601	12
1000	1