I am trying to calculate the area of circle. i take the value in one textbox named as textBox1 and I have to show the calculated answer into another textbox named as textBox2. I did the first part but don't know how to do the second one. Plz guide...

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

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

    int radius;
    const double PI = 3.14159;
    double area; 

    private void textBox1_TextChanged(object sender, EventArgs e)
    {

    }

    private void button1_Click(object sender, EventArgs e)
    {
        radius = int.Parse(textBox1.Text);
        area = PI * radius * radius;

        textBox2.Text = area;    /// here it is showing error now        
    }

    private void textBox2_TextChanged(object sender, EventArgs e)
    {

    }
}
}

```