Dairenin alanını ve çevresini bulma

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
 public partial class Form1 : Form
 {
 public Form1()
 {
 InitializeComponent();
 }

 private void button1_Click(object sender, EventArgs e)
 {
 const float pi = 3.14f;
 float cevre, alan;
 int r;
 r = Convert.ToInt32(textBox1.Text);
 alan = pi * r * r;
 cevre = 2 * pi * r;
 textBox2.Text = alan.ToString();
 textBox3.Text = cevre.ToString();
 }
 }
}

KAYNAK: http://www.gorselprogramlama.com/alancevre-hesaplama-c-windows-form-application/