TextBox Control

protected void Button1_Click(object sender, EventArgs e)
{
TextBox1.Text = "You have clicked the button";
TextBox4.Text = "This is a multi line textbox. This is a multi line textbox. This is a multi line textbox. This is a multi line textbox. ";

TextBox3.Text = TextBox2.Text;
}
protected void TextBox1_TextChanged(object sender, EventArgs e)
{
TextBox1.Text = "The Text is changed.";

}