How to set up a C# textbox to only allow input of numbers?

To restrict the text box to only allow numeric input, you can add code to the KeyPress event of the text box to check if the character entered by the user is a number. Here is an example code:

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar))
    {
        e.Handled = true;
    }
}

In the code above, the KeyPress event is triggered when the user presses a key on the keyboard. We first check in the event handler if the pressed key is a control key or a number key. If it is not a number key, we set the Handled property to true, indicating that the key should not be processed.

By setting this up, users are only able to input numbers in the text box, all other characters will be disregarded.