Parsing a string C# (Possibly with Regex)

Question

I am trying to parse a line of code for a mathematical operation.

Such as: 4+18/(9-3)

I want the sections to be: 4, +, 18, /, (, 9, -, 3, and ). So basically, all numbers, operators, and parenthesis.

If I use split with delimiters it removes the delimiter upon finding it. So if I use my operators as delimiters, well then they're removed.

I tried using Regex.split and it INCLUDES the operator, but not how I want it. It produces results like 4+, since it includes the 4 and the plus.

Here's what I've been trying:

        string convert = "4+8/(9-3)";

        string[] parts = Regex.Split(convert, @"(?<=[-+*/])");

You can use Regex to parse a string, but you cannot use regex to parse syntax. You would be better off using a math expression parser/evaluator. — Prime
– Prime, Commented Mar 31, 2018 at 23:46
But, to answer your question anyway, ([\d\.]+|[()e^/%x*+-]) should work. (example) — Prime
– Prime, Commented Mar 31, 2018 at 23:51
If you plan to work with integers only, Regex.Split(convert, @"(\D)");. But it will not work as an end solution. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Mar 31, 2018 at 23:57

Prime · Accepted Answer · 2018-04-01 00:12:44Z

4

As per my comment if you intend to use this to evaluate a math expression you should not use Regex as you cannot have any syntactic or semantic understanding of a string you're parsing.

If you're not intending to do that, this should work fine

([\d\.]+|[()e^/%x*+-])

Regexr example

Dotnetfiddle example

edited Apr 1, 2018 at 0:12

answered Apr 1, 2018 at 0:04

Prime

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3 Comments

Prime Over a year ago

@Aran-Fey You're correct, changed from Regex.Split to Regex.Matches

Birdman Over a year ago

This added some extra "" empty string entries for me but I just created a quick loop to remove them. Not sure if I did something wrong to include them, but once the empty strings were removed which was easy enough the results so far from my testing have been desirable. Thanks.

Prime Over a year ago

@Birdman It's because of how Regex.Split works, if you check the Dotnetfiddle example I use Regex.Matches and loop through the matches it returns instead.

nicael · Accepted Answer · 2018-04-01 00:03:38Z

-1

Well, I guess the problem could be solved with the help of the following regex.

[-+*/\(\)]|\d+

edited Apr 1, 2018 at 0:03

answered Mar 31, 2018 at 23:48

nicael

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7 Comments

Aran-Fey Over a year ago

Nope. This splits numbers into single digits.

Aran-Fey Over a year ago

Nope. Now it duplicates every character. And even if you change that capture group to a non-capturing group it still would split numbers into single digits. Please test your regex; this is getting silly.

nicael Over a year ago

"it still would split numbers into single digits" - how is that, @Aran?

Aran-Fey Over a year ago

Well, because it doesn't matter if you use \d or \d+ in a lookbehind. After the regex passes the first digit, the lookbehind sees a digit and the number is split into two, + or not.

nicael Over a year ago

@Aran I didnt think of lookbehind but now im actually not sure why op used it all

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