Ok, now I've got another small problem.

Here's my code:

public partial class Form1 : Form
{
int num1, num2;

public Form1()
{
InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{

}

private void btn_0_Click(object sender, EventArgs e)
{
txt_Calc.Text = "0";
}

private void btn_1_Click(object sender, EventArgs e)
{
txt_Calc.Text = "1";
}

private void btn_2_Click(object sender, EventArgs e)
{
txt_Calc.Text = "3";
}

private void btn_3_Click(object sender, EventArgs e)
{
txt_Calc.Text = "4";
}

private void btn_5_Click(object sender, EventArgs e)
{
txt_Calc.Text = "5";
}

private void btn_6_Click(object sender, EventArgs e)
{
txt_Calc.Text = "6";
}

private void btn_7_Click(object sender, EventArgs e)
{
txt_Calc.Text = "7";
}

private void btn_8_Click(object sender, EventArgs e)
{
txt_Calc.Text = "8";
}

private void btn_9_Click(object sender, EventArgs e)
{
txt_Calc.Text = "9";
}

private void btn_add_Click(object sender, EventArgs e)
{
int.TryParse(txt_Calc.Text, out num1);
MessageBox.Show(num1.ToString());

}
}

With this code I'm able to click on each NUMBERED button and display it's value in the textbox. But each time I click on another NUMBERED button, the previous value in the textbox gets replaced by the current number. So basically, I can only enter one number.
Please help.