Get value from TextBox : TextBox : GUI Windows Form C# Source Code

    
 
using System;
using System.Drawing;
using System.Windows.Forms;

public class InterestCalculator : Form {

    Button buttonCalculate  = new Button();

    TextBox textBoxPrincipal = new TextBox();
    TextBox textBoxRate = new TextBox();
    TextBox textBoxInterest = new TextBox();

    Label labelPrincipal = new Label();
    Label labelRate = new Label();
    Label labelInterest = new Label();

    public InterestCalculator() {
        buttonCalculate.Location = new Point(50, 100);
        buttonCalculate.Text = "Calculate";

        buttonCalculate.Click += new System.EventHandler(this.buttonCalculate_Click);

        this.Controls.Add(buttonCalculate);

        textBoxPrincipal.Location = new Point(10, 20);
        textBoxPrincipal.Size = new Size(150, 10);
        textBoxPrincipal.Text = "100000.00";
        this.Controls.Add(textBoxPrincipal);

        textBoxRate.Location = new Point(10, 60);
        textBoxRate.Size = new Size(150, 10);
        textBoxRate.Text = "0.15";
        this.Controls.Add(textBoxRate);

        textBoxInterest.Location = new Point(10, 150);
        textBoxInterest.Size = new Size(150, 10);
        textBoxInterest.Text = "15000.00";
        this.Controls.Add(textBoxInterest);

        labelPrincipal.Location = new Point(10, 5);
        labelPrincipal.Size = new Size(144, 15);
        labelPrincipal.Text = "Principal";
        this.Controls.Add(labelPrincipal);

        labelRate.Location = new Point(10, 45);
        labelRate.Size = new Size(144, 15);
        labelRate.Text = "Rate";
        this.Controls.Add(labelRate);

        labelInterest.Location = new Point(10, 135);
        labelInterest.Size = new Size(144, 15);
        labelInterest.Text = "Interest";
        this.Controls.Add(labelInterest);
    }

    private void buttonCalculate_Click(object sender, System.EventArgs e) {
        double prin = Convert.ToDouble(textBoxPrincipal.Text);
        double rate = Convert.ToDouble(textBoxRate.Text);
        double amt = prin * rate;
        textBoxInterest.Text = amt.ToString("f2");
    }

    public static void Main(string[] args) {
        Application.Run(new InterestCalculator());
    }
}