CODEWITHSUNDEEP
c#.netregex
Subodh
Subodh

Reputation: 75

Regex Pattern to Parse the formula bar

I am implementing the formula bar in which there can be any operation with two values like:

SUB ( DIV ( ADD (2,5), 4.5 ), AVG (3,4) )

So here I need to first call ADD operation as its most inner operation, then DIV it by some fraction, then calculate the AVG and in last SUB both the values, so there can be any formula user can put on formula bar.

I am trying to write recursive function for that but before that I need to parse it properly. I could not figure out how to write regex for this kind of pattern..

Any ideas please?

Upvotes: 1

Views: 148

Answers (1)

Ronald Zarīts
Ronald Zarīts

Reputation: 12699

If what you are trying to do is break the expression into subexpressions and get the contents of a subexpression between parenthesis - you cannot do this with regular expressions. Regular expressions cannot handle the parenthesis matching problem.

You'd need to devise another algorithm to do that - a stack based approach (push on opening parenthesis, pop on closing parenthesis) could be one approach.

Here's a related question about this issue: Regular Expression to match outer brackets

However, you could use a regex to validate/parse leaf expressions (the ones with no nested expressions) in the expression tree, once you've got your expression broken down.

EDIT: while the above is true for regular expressions in general as a language (as taught in CS classes), libraries have made enhancements to the language to allow this. Perl has done this for a long time, and it seems it's possible in .NET as well. Here's a post explaining Balanced Matching in the .NET Regex implementation.

http://blogs.msdn.com/b/bclteam/archive/2005/03/15/396452.aspx

Upvotes: 2

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