Swap two numbers without using a third variable

Step 1: Design Page – SwapNumbers.aspx

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

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Swap Two Numbers Without Third Variable - 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>Swap Two Numbers (Without Using Third Variable)</h2>
            
            <asp:Label ID="lblFirst" runat="server" Text="Enter First Number:"></asp:Label><br />
            <asp:TextBox ID="txtFirst" runat="server" CssClass="form-control"></asp:TextBox><br />

            <asp:Label ID="lblSecond" runat="server" Text="Enter Second Number:"></asp:Label><br />
            <asp:TextBox ID="txtSecond" runat="server" CssClass="form-control"></asp:TextBox><br />

            <asp:Button ID="btnSwap" runat="server" Text="Swap Numbers" CssClass="btn" OnClick="btnSwap_Click" /><br />

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

Step 2: Backend Logic – SwapNumbers.aspx.cs

using System;

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

    protected void btnSwap_Click(object sender, EventArgs e)
    {
        int num1, num2;
        bool valid1 = int.TryParse(txtFirst.Text.Trim(), out num1);
        bool valid2 = int.TryParse(txtSecond.Text.Trim(), out num2);

        if (!valid1 || !valid2)
        {
            lblResult.Text = "Please enter valid numbers.";
            lblResult.ForeColor = System.Drawing.Color.Red;
            return;
        }

        // Swapping logic without using a third variable
        num1 = num1 + num2;  // Step 1: Add both numbers
        num2 = num1 - num2;  // Step 2: Subtract second from sum to get first
        num1 = num1 - num2;  // Step 3: Subtract new second from sum to get second

        lblResult.Text = $"After swapping:<br/>First Number = {num1}<br/>Second Number = {num2}";
        lblResult.ForeColor = System.Drawing.Color.Green;
    }
}

Real-Time Example Flow

Open the page SwapNumbers.aspx.
Enter values — e.g., num1 = 10, num2 = 20.
Click “Swap Numbers”.
The output will display:

After swapping:
First Number = 20
Second Number = 10

Explanation

Step	Description
Step 1	num1 = num1 + num2 adds both numbers.
Step 2	num2 = num1 - num2 gives the original value of num1.
Step 3	num1 = num1 - num2 gives the original value of num2.
Result	Both numbers are swapped without using a third variable.

Sample Input / Output

Input	Output
10, 20	20, 10
45, 100	100, 45
5, 8	8, 5