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Regular Expression for Currency

I am trying to come up with a regular expression to validate some dynamic controls.  

I need to be able to validate against certain inputs, such as:

Text box can be empty - this is fine, display no error
Text box can have a whole number e.g. 100 - this is fine, display no error
Text box can have a decimal but must be 2 decimal places maximum (1 is allowed) - display error only if greater than 3 decimal places
Text box should not contain just a decimal point - otherwise display an error
Text box should not contain any other characters than digits and 1 decimal point - otherwise display an error

isValid = Regex.IsMatch(item.ItemAmount.ToString(), "^[0-9]+(.[0-9]{1,2})?$");

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The above is what I currently have but it doesn't seem to work, on validation it fails for 100, 100.20 etc.
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angus_young_acdc
Asked:
angus_young_acdc
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1 Solution
 
käµfm³d 👽Commented:
Try:

^\d+(?:\.\d{1,2})?$

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angus_young_acdcAuthor Commented:
Hi Kaufmed,

That one kind of works, if I just enter a '.' it doesn't produce an error.
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käµfm³d 👽Commented:
That should not be the case. The leading "\d+" requires at least one digit--even if you don't enter anything else. However, thinking about this now I did not cover the possibility of no input. The previous needs to be modified:

^(?:\d+(?:\.\d{1,2})?)?$

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e.g.

Screenshot
And I totally overlooked your code. In actuality, we pretty much have the same pattern. The only issue with yours is that you did not escape the dot, and dot matches anything. If you escape the dot, and make the whole pattern (excluding start-of-string and end-of-string) optional, then yours should work as well.
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