Pascal’s Triangle in C# WebForms

Sandhiya Priya
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Article

Concept: Pascal’s Triangle

Pascal’s Triangle is a triangular array of numbers where each number is the sum of the two numbers directly above it.

Example for 5 rows

WebForms Real-Time Example

ASPX Page (PascalTriangle.aspx)

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="PascalTriangle.aspx.cs" Inherits="WebApp.PascalTriangle" %>

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Pascal’s Triangle Example</title>
</head>
<body>
    <form id="form1" runat="server">
        <div style="font-family:Arial; margin:50px;">
            <h2>Generate Pascal’s Triangle</h2>
            <asp:Label ID="Label1" runat="server" Text="Enter number of rows:" />
            <asp:TextBox ID="txtRows" runat="server"></asp:TextBox>
            <asp:Button ID="btnGenerate" runat="server" Text="Generate" OnClick="btnGenerate_Click" />
            <br /><br />
            <asp:Label ID="lblResult" runat="server" />
        </div>
    </form>
</body>
</html>

Code-Behind (PascalTriangle.aspx.cs)

using System;
using System.Text;

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

        protected void btnGenerate_Click(object sender, EventArgs e)
        {
            int rows;
            if (int.TryParse(txtRows.Text, out rows) && rows > 0)
            {
                lblResult.Text = GeneratePascalTriangle(rows);
            }
            else
            {
                lblResult.Text = "Please enter a valid positive number.";
            }
        }

        private string GeneratePascalTriangle(int rows)
        {
            int[,] triangle = new int[rows, rows];
            StringBuilder sb = new StringBuilder();

            for (int i = 0; i < rows; i++)
            {
                for (int j = 0; j <= i; j++)
                {
                    // First and last values in a row are 1
                    if (j == 0 || j == i)
                        triangle[i, j] = 1;
                    else
                        triangle[i, j] = triangle[i - 1, j - 1] + triangle[i - 1, j];

                    sb.Append(triangle[i, j] + " ");
                }
                sb.Append("<br/>");
            }

            return sb.ToString();
        }
    }
}

Explanation

txtRows → User enters the number of rows.
When the Generate button is clicked:
- The code calls GeneratePascalTriangle(rows) method.
- It builds Pascal’s triangle using a 2D array.
- Each row starts and ends with 1.
- Every middle element = sum of the two numbers above it.
- The result is displayed in lblResult using <br/> for line breaks.

Output Example

If the user enters 5, output will be: