Hey everyone! Happy New Year!

I am trying to hone my programming skills by writing simple applications. I created a very simple currency converter program (hard-coded exchange rates....so nothing special). I first created it as a console app, and then in WPF.

Anyway, I ran into an issue with the textbox that takes input. I wasn't sure what would be the best way to keep letters from being entered. After looking online at regular expressions, I wrote a basic regex using an if statement to keep invalid input from being entered:


If the input has letters, then a messagebox is prompted (after pressing a button) and I have that button's method set to clear the textbox.

*****So basically, the program works 100% properly, but I was wondering if using Regex was the "best" move as opposed to trying to implement a try-catch, which quite honestly, I do not understand how to use completely. I was reading something about SQL queries vs. LINQ (speed of returning results), etc. and was wondering if regex vs. try-catch was similar.

*If anyone wants to see some of the code, just let me know which parts you want to see or the whole program.

You are trying to ensure that only numbers are entered (with the appropriate decimal specifier, if needed). Regex and Try/Catch are slow ways to do this, just use TryParse:

double value = 0.0;
if (Double.TryParse(myTextBox.Text, out value)) {
    // it is convertable to a double, so we are good and the value is in 'value'
} else {
    // it is not convertable to a double: Error, danger Will Robinson!

of course you can use other types (Int32, Decimal, etc.) just replace the appropriate types :)

or switch to a masked text box where you can set a mask to filter out letters

Ah, TryParse looks like a better way! Thanks Momerath!

Tinstaafl, thanks for suggesting the masked textbox. I didn't know about that functionality.

Thanks for the quick responses. Sorry for getting back to you all so late.

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