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c#regexcurrency-formatting

Regex for currency value

I have this regex that is working perfect to match currency values for U.S.A format ($1.50): 

Regex money = new Regex(@"\w\^\$(\d{1,3}(\,\d{3})*|(\d+))(\.\d{2})?$");

I'd like to have some help to UNDERSTAND how to build a regex like that, I need to change the format for my country, like change the $ for R$.

I'm looking on msdn topics but nothing worked so far...

Solution

  • Your question has three parts, and to me it sounds like it is mostly about "learning how to fish", which is great.

    **A. The Regex You Want **

    Based on the comments, you are looking for this (see demo):

    ^R\$\d+(?:\.\d{3})*,\d{2}$

    B. Explanation of the Regex

    This is a relatively simple regex, and for this you can read an automatically-generated explanation. Several sites do this. Here is one (it will display better on the original site). 

    NODE                     EXPLANATION
--------------------------------------------------------------------------------   \w                       word characters (a-z, A-Z, 0-9, _)
--------------------------------------------------------------------------------   \^                       '^'
--------------------------------------------------------------------------------   \$                       '$'
--------------------------------------------------------------------------------   (                        group and capture to \1:
--------------------------------------------------------------------------------
    \d{1,3}                  digits (0-9) (between 1 and 3 times
                             (matching the most amount possible))
--------------------------------------------------------------------------------
    (                        group and capture to \2 (0 or more times
                             (matching the most amount possible)):
--------------------------------------------------------------------------------
      \,                       ','
--------------------------------------------------------------------------------
      \d{3}                    digits (0-9) (3 times)
--------------------------------------------------------------------------------
    )*                       end of \2 (NOTE: because you are using a
                             quantifier on this capture, only the
                             LAST repetition of the captured pattern
                             will be stored in \2)
--------------------------------------------------------------------------------    |                        OR
--------------------------------------------------------------------------------
    (                        group and capture to \3:
--------------------------------------------------------------------------------
      \d+                      digits (0-9) (1 or more times
                               (matching the most amount possible))
--------------------------------------------------------------------------------
    )                        end of \3
--------------------------------------------------------------------------------   )                        end of \1
--------------------------------------------------------------------------------   (                        group and capture to \4 (optional
                           (matching the most amount possible)):
--------------------------------------------------------------------------------
    \.                       '.'
--------------------------------------------------------------------------------
    \d{2}                    digits (0-9) (2 times)
--------------------------------------------------------------------------------   )?                       end of \4 (NOTE: because you are using a
                           quantifier on this capture, only the LAST
                           repetition of the captured pattern will be
                           stored in \4)
--------------------------------------------------------------------------------   $                        before an optional \n, and the end of the
                           string

    C. How Can I Learn to Build a Regex Like That

    Here are the resources I recommend.

    1. Books: Mastering Regular Expressions (3rd Ed), the Regex Cookbook

    2. Websites: regular-expressions.info, RexEgg, FAQ on SO

    3. Tools: RegexBuddy (commercial but outstanding debugger), regex101.com, Debuggex.com