using System;
using System.Drawing;
using System.Windows.Forms;
using System.Text.RegularExpressions;

class Program01 : Form {	
	TextBox rBox = new TextBox();
	TextBox hBox = new TextBox();
	Label rLabel = new Label();
	Label hLabel = new Label();
	Button szamitButton = new Button();
	TextBox resBox = new TextBox();
	Program01() {
		initComponent();
	}
	public void initComponent() {
		rBox.Location = new Point(120, 10);
		hBox.Location = new Point(120, 40);
		rLabel.Location = new Point(10, 10);
		hLabel.Location = new Point(10, 40);
		resBox.Location = new Point(120, 80);
		szamitButton.Location = new Point(10, 80);
		rLabel.Text = "Sugár";
		hLabel.Text = "Magasság";
		szamitButton.Text = "Számít";
		szamitButton.Click += new EventHandler(SzamitClick);
		rBox.TextChanged += new EventHandler(rTextChanged);
		hBox.TextChanged += new EventHandler(hTextChanged);
		
		this.Controls.Add(rBox);
		this.Controls.Add(hBox);
		this.Controls.Add(rLabel);
		this.Controls.Add(hLabel);
		this.Controls.Add(szamitButton);
		this.Controls.Add(resBox);
		this.Size = new Size(400, 300);
		this.Show();		
	}
	public void rTextChanged(object sender, EventArgs e) {
		if(!IsValid(rBox.Text)) {
			rBox.BackColor = Color.Red;
		}else {
			rBox.BackColor = Color.White;
		}
	}
	public void hTextChanged(object sender, EventArgs e) {
		if(!IsValid(hBox.Text)) {
			hBox.BackColor = Color.Red;
		}else {
			hBox.BackColor = Color.White;
		}		
	}
	public bool IsValid(string value) {
		return Regex.IsMatch(value, @"^[0-9]*$");
    }
	
	
	public void SzamitClick(object sender, EventArgs e) {
		string sugarStr = rBox.Text;
		string magassagStr = hBox.Text;
		double sugar = Convert.ToDouble(sugarStr);
		double magassag = Convert.ToDouble(magassagStr);
		double terfogat = (1.0/3.0) * Math.Pow(sugar, 2) *
			Math.PI * magassag;
		resBox.Text = terfogat.ToString();
	}
	public static void Main() {
		Application.Run(new Program01());
	}
}