Reverse a string without using built-in functions.

Step 1: Design Page – ReverseString.aspx

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

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Reverse String Without Using Built-in Function</title>
    <style>
        body {
            font-family: Arial;
            background-color: #f0f2f5;
            margin: 50px;
        }
        .container {
            width: 450px;
            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;
            width: 100%;
        }
        .result {
            margin-top: 15px;
            font-weight: bold;
            color: #333;
            text-align: center;
        }
    </style>
</head>
<body>
    <form id="form1" runat="server">
        <div class="container">
            <h2>Reverse a String (Without Built-in Function)</h2>

            <asp:Label ID="lblString" runat="server" Text="Enter a String:"></asp:Label><br />
            <asp:TextBox ID="txtInput" runat="server" CssClass="form-control" placeholder="Example: Sandhiya"></asp:TextBox><br />

            <asp:Button ID="btnReverse" runat="server" Text="Reverse String" CssClass="btn" OnClick="btnReverse_Click" /><br />

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

Step 2: Backend Logic – ReverseString.aspx.cs

using System;

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

    protected void btnReverse_Click(object sender, EventArgs e)
    {
        string input = txtInput.Text.Trim();

        if (string.IsNullOrEmpty(input))
        {
            lblResult.Text = "Please enter a string.";
            lblResult.ForeColor = System.Drawing.Color.Red;
            return;
        }

        string reversed = ReverseWithoutBuiltin(input);

        lblResult.Text = $"Reversed String: {reversed}";
        lblResult.ForeColor = System.Drawing.Color.Green;
    }

    private string ReverseWithoutBuiltin(string str)
    {
        char[] chars = str.ToCharArray();
        string rev = "";

        for (int i = chars.Length - 1; i >= 0; i--)
        {
            rev += chars[i];
        }

        return rev;
    }
}

Real-Time Example Flow

Open ReverseString.aspx in your browser.
Enter a string — e.g., Sandhiya
Click “Reverse String”
Output displays:

Reversed String: ayihdnaS

Explanation

Step	Description
1	Input a string from user.
2	Convert string into character array.
3	Loop backward from end to start.
4	Concatenate each character into a new string.
5	Display reversed string in label.

Sample Input / Output

Input	Output
Sandhiya	ayihdnaS
Hello	olleH
Level	leveL
Welcome	emocleW