How to validate for numeric operand in textbox

Question

I have the folllowing code for only numbers in the texbox, but would also like to include only numeric operations too (+,-, *, etc). How would you code for this please.

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

Possible duplicate of [Parse Math Expression](http://stackoverflow.com/questions/3972854/parse-math-expression) — Dour High Arch, May 27 '16 at 23:48

score 0 · Answer 1 · answered May 28 '16 at 00:17

If you only want digits and +, -, *, / you should use something like this:

private char[] validChars = {'+', '-', '*', '/'};

private void txtCalculation_KeyPress(object sender, KeyPressEventArgs e) {        
    e.Handled = !char.IsDigit(e.KeyChar) && !char.IsControl(e.KeyChar) && !Array.Exists(validChars, e.KeyChar);
}

The array validChars defines additional chars which are valid. And with the Array.Exists method you are able to check if the array contains a value specified by the second parameter of the method - in this case e.KeyChar.

How to validate for numeric operand in textbox

1 Answers1