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!

Vulpes · Answer

You could also combine the checks for negative numbers with the existing checks for invalidity. One other thing you could do is to place the input focus back to the textbox where the problem lies: 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) || width ) { MessageBox.Show(The width is invalid. Notification MessageBoxButtons.OK MessageBoxIcon.Error); this.tbWidth.Focus(); return; } if (!double.TryParse(this.tbHeight.Text.Trim() out height) || height ) { MessageBox.Show(The height is invalid. Notification MessageBoxButtons.OK MessageBoxIcon.Error); this.tbHeight.Focus(); return; } if (!double.TryParse(this.tbLength.Text.Trim() out length) || length ) { MessageBox.Show(The length is invalid. Notification MessageBoxButtons.OK MessageBoxIcon.Error); this.tbLength.Focus(); return; } }

Faraz khan · Answer

you can use below statement for each of your value if (_value 0 ) { MessageBox .Show( The _value is invalid.  Notification  MessageBoxButtons .OK MessageBoxIcon .Error); return; }