CODEWITHSUNDEEP
c#regexwinforms
Beau Altman
Beau Altman

Reputation: 37

Input String is not correct format when trying to type in a hyphen first

I am trying to put a negative number in a textbox, however whenever i click on the textbox and try to type for they hyphen it creates the error, also I don't want it to create this same error if i accidentally leave the textbox blank. as it has done before

TextBox tbox = this.Controls.Find("Team" + r.ToString() + "Q" + c.ToString(), true).FirstOrDefault() as TextBox;
int t1 = Convert.ToInt32(tbox.Text);
if (r == 1) team1score += t1;`

Upvotes: 0

Views: 259

Answers (1)

Jim Mischel
Jim Mischel

Reputation: 134055

Yes, it's probably because when you type -, the CalculateTotals method is called and it tries to convert - to an integer, and fails. You don't show how you're doing the conversion, which is the most important part of your code. You probably should do something like this:

int myInt;
if (!int.TryParse(senderTB.Text, out myInt))
{
    // The value in the textbox isn't an integer.
    // Use 0 as the default.
    myInt = 0;
}

That's not entirely correct, though, because the user might type something like 4000000000, which is larger than an int.

A quick fix would be to modify your regular expression so that it requires at least one number:

Regex reg = new Regex(@"^-?[0-9]+$");

Replacing the * with a + won't allow just a hyphen to match. This will fix your immediate problem, but it's not complete error checking. But it might be good enough for your purposes.

In general, you can easily use regular expressions to validate the form of a signed integer (i.e. an optional hyphen followed by one or more digits), but it's very difficult to use regular expressions to make sure the number is within the range of a signed integer. Making sure that the number is not less than -2147483648 or greater than 2147483647 is rather difficult to do with regular expressions.

You probably want a combination of the approaches: use the regular expression to prevent the user from typing illegal characters into the text box, and use int.TryParse to validate the number in your computeTotals method. And rather than defaulting to a value of 0, have the program display a message box informing the user of the error.

Upvotes: 2

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