Add, Remove, and Search elements in a List

Step 1: Design Page – ListOperations.aspx

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

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>List Operations (Add, Remove, Search) - Real Time Example</title>
    <style>
        body {
            font-family: Arial;
            background-color: #f4f6fc;
            margin: 50px;
        }
        .container {
            width: 550px;
            margin: auto;
            background: #fff;
            border-radius: 10px;
            box-shadow: 0px 0px 10px #ccc;
            padding: 25px;
        }
        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;
            border-radius: 5px;
            cursor: pointer;
            width: 32%;
        }
        .btn:hover {
            background-color: #5b68a1;
        }
        .button-group {
            display: flex;
            justify-content: space-between;
            margin-top: 15px;
        }
        .result {
            margin-top: 20px;
            font-weight: bold;
            color: #333;
            text-align: center;
            white-space: pre-line;
        }
        hr {
            margin-top: 15px;
            border: 0.5px solid #ccc;
        }
    </style>
</head>
<body>
    <form id="form1" runat="server">
        <div class="container">
            <h2>List Operations (Add / Remove / Search)</h2>

            <asp:Label ID="lblInput" runat="server" Text="Enter a Number:"></asp:Label><br />
            <asp:TextBox ID="txtNumber" runat="server" CssClass="form-control" placeholder="Example: 25"></asp:TextBox>

            <div class="button-group">
                <asp:Button ID="btnAdd" runat="server" Text="Add" CssClass="btn" OnClick="btnAdd_Click" />
                <asp:Button ID="btnRemove" runat="server" Text="Remove" CssClass="btn" OnClick="btnRemove_Click" />
                <asp:Button ID="btnSearch" runat="server" Text="Search" CssClass="btn" OnClick="btnSearch_Click" />
            </div>

            <hr />

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

Step 2: Backend Logic – ListOperations.aspx.cs

using System;
using System.Collections.Generic;

public partial class ListOperations : System.Web.UI.Page
{
    // Using a static list to persist data across postbacks
    private static List<int> numbers = new List<int>();

    protected void Page_Load(object sender, EventArgs e)
    {
    }

    // Add Element
    protected void btnAdd_Click(object sender, EventArgs e)
    {
        if (int.TryParse(txtNumber.Text.Trim(), out int num))
        {
            numbers.Add(num);
            lblResult.Text = $"Number {num} added successfully!\n\nCurrent List: {string.Join(", ", numbers)}";
            lblResult.ForeColor = System.Drawing.Color.Green;
        }
        else
        {
            lblResult.Text = "Please enter a valid number.";
            lblResult.ForeColor = System.Drawing.Color.Red;
        }
    }

    // Remove Element
    protected void btnRemove_Click(object sender, EventArgs e)
    {
        if (int.TryParse(txtNumber.Text.Trim(), out int num))
        {
            if (numbers.Remove(num))
            {
                lblResult.Text = $"Number {num} removed successfully!\n\nCurrent List: {string.Join(", ", numbers)}";
                lblResult.ForeColor = System.Drawing.Color.Green;
            }
            else
            {
                lblResult.Text = $"Number {num} not found in the list.";
                lblResult.ForeColor = System.Drawing.Color.OrangeRed;
            }
        }
        else
        {
            lblResult.Text = "Please enter a valid number.";
            lblResult.ForeColor = System.Drawing.Color.Red;
        }
    }

    // Search Element
    protected void btnSearch_Click(object sender, EventArgs e)
    {
        if (int.TryParse(txtNumber.Text.Trim(), out int num))
        {
            if (numbers.Contains(num))
            {
                lblResult.Text = $"Number {num} found in the list.\n\nCurrent List: {string.Join(", ", numbers)}";
                lblResult.ForeColor = System.Drawing.Color.Green;
            }
            else
            {
                lblResult.Text = $"Number {num} not found.\n\nCurrent List: {string.Join(", ", numbers)}";
                lblResult.ForeColor = System.Drawing.Color.OrangeRed;
            }
        }
        else
        {
            lblResult.Text = "Please enter a valid number.";
            lblResult.ForeColor = System.Drawing.Color.Red;
        }
    }
}

Real-Time Example Flow

Run your project and open ListOperations.aspx.

Enter a number, e.g. 10, and click Add.
Output

Number 10 added successfully!
Current List: 10

Enter another number, e.g. 20, and click Add.
Output

Number 20 added successfully!
Current List: 10, 20

Enter 10 and click Search.
Output

Number 10 found in the list.
Current List: 10, 20

Enter 10 and click Remove.
Output

Number 10 removed successfully!
Current List: 20

Explanation

Operation	Description
Add	Adds a new number to the List using List.Add().
Remove	Removes a specific number using List.Remove().
Search	Checks if a number exists in the List using List.Contains().
Static List	Maintains the list data across postbacks (web page refreshes).

Example Input / Output Table

Operation	Input	Output
Add	15	Number 15 added successfully! Current List: 15
Add	30	Number 30 added successfully! Current List: 15, 30
Search	15	Number 15 found in the list.
Search	25	Number 25 not found.
Remove	15	Number 15 removed successfully! Current List: 30

Algorithm

1. Initialize an empty List<int>.
2. If Add:
      Convert input to integer and add to list.
3. If Remove:
      Check if number exists, then remove.
4. If Search:
      Check if number exists using Contains().
5. Display updated list to user.