How do I parse an integer, using the rule that +5 is not valid but 5 is?

Question

My program asks the user to input a number from 1 - 10 in a text box in. When I the user inputs the number I have it converted into an int, by using this:

if (!int.TryParse(inputBox.Text, out input))

I used the ! because if the number cannot be TryParse'd into a int it throws an error to the user.

This works, until I enter a number that begins with a +, for example +5, or +1. It isn't catching the fact that there is a + in front of the int. If I enter more than one + it throws an error like it should.

How would someone make an error proofing line(s) of code that checks for this type of input?

Answer 1

I think you want to allow 1-10 without the positive sign (+).

int number;
var input = numberTextBox.Text;
if (!input.StartsWith("+") && int.TryParse(input, out number))
{
    //valid input, check if it's between 1-10
}

But I think the requirement is really strange. "+10" is considered the same as "10", it is a valid input.