Tutorial :Regex that looks for a certain number of digits in a string?



Question:

When a user submits a form I need to make sure that the input contains at least a minimum number of digits. The problem is that I don't know what format the input will be in. The digits likely won't be in a row, and might be separated by letters, punctuation, spaces, etc. I don't care about the rest of the string.

I'd like to check this with a RegularExpressionValidator but I'm not quite sure how to write the regex.

I guess this would be similar to a phone number regex, but a phone number at least has some common formats.


Solution:1

The following will match an input string containing at least n digits:

Regex.IsMatch(input, @"(\D*\d){n}");  

where n is an integer value.

A short explanation:

  • \D* matches zero or more non-digit chars (\D is a short hand for [^0-9] or [^\d]);
  • so \D*\d matches zero or more non-digit chars followed by a digit;
  • and (\D*\d){n} groups, and repeats, the previous n times.


Solution:2

I would approach it something like this:

Regex.IsMatch(input, @"^(.*[0-9].*){10}$");

In words, this would search for 10 digits, each of which are surrounded by 0 or more characters. Since the .* are greedy, any additional digits would be matched by them as well.

Anyway, check out http://regexlib.com/RETester.aspx It can be really hard to write a regular expression without something to test against.


Solution:3

in order to have at least n digits, you need to use following regex:

(\D*\d){n,}

Regex (\D*\d){n} will match exactly n digits.

Regards, Karlo.


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