how to prevent negative number input from user in textbox

Question

This is what I have:

private void btnCompute_Click(object sender, EventArgs e)

       {

double width = 0;

     

double length = 0;

           

double height = 0;

           

if (!double.TryParse(this.tbWidth.Text.Trim(), out width))

            {

               

MessageBox.Show("The width is invalid.", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);

               

return;

            }

           

if (!double.TryParse(this.tbHeight.Text.Trim(), out height))

            {

               

MessageBox.Show("The height is invalid.", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);

               

return;

            }

           

if (!double.TryParse(this.tbLength.Text.Trim(), out length))

            {

               

MessageBox.Show("The length is invalid.", "Notification", MessageBoxButtons.OK, MessageBoxIcon.Error);

               

return;

            }

It accepts negative numbers, but I want to able to show an error message when a negative number is entered for the width, height, or length.

Any help is greatly appreciated, Thanks!