How make it decimal and how to stop the error message

Question

Hi!

I do write this code. But I would like to see the number I enter in the textbox be decimal. How can I do it please.

Other point strange, when I am trying to delete my textbox that should make operation. When the last number is deleted I receive a error message:

Input string was not in a correct format. 

 

private void quantidadeFactu_KeyUp(object sender, KeyEventArgs e)

{

float quantidadeFact;

float precoFact;

float totFact;

quantidadeFact = Convert.ToInt32(quantidadeFactu.Text);//for example in this quantitity textbox when I delete until the latest number. The error message appear.

precoFact = Convert.ToInt32(precosaidaFactu.Text);

totFact = quantidadeFact * precoFact;

totalFactu.Text = totFact.ToString();

}