Regex doesn't work as I need

Question

I need to validate an account number. It is supposed to have only digits and have 9 or 10 characters. I tried this:

return Regex.IsMatch(id, "[0-9]{9,10}");

But this is not working correctly, as it returns true in case the number is "1234567890blah". Could you please help, as I am not that good with regex?

Thanks.

Answer 1

You need to indicate that the digits must be the entire string. Put ^ at the start to indicate that it must be the start of the string and $ to indicate that it must be the end.

return Regex.IsMatch(id, "^[0-9]{9,10}$");

See Regular Expression Anchors for more details.

Answer 2

Modify by using ( Add start and end caracter, ^ and $ caracter)

return Regex.IsMatch(id, "^[0-9]{9,10}$");