c# split arithmetic expression to string[]

Question

I have a simple arithmetic expression containing integers, parentheses, and +-*/. Like this:

((1+33)()(4+(3-5)))

What I need to do is split this expression to the string[] like this:

{(, (, 1, +, 33, ), (, ), (, 4, +, (, 3, -, 5, ), ), )}

I am trying to do it with Regex class

public string[] SplitString(string str)
{
     return Regex.Split(str, "(?<=[()-+*/])|(?=[()-+*/])");
}

But output data is not quite right:

{(, (, 1, +, 33, ), (, ), (, 4, +, (, **3-5**, ), ), )}

You can compute the result without splitting it. Is this what you are after ? — Zein Makki, Jul 23 '16 at 11:49
Note that `)-+` create a range in your char class that matches more than you might expect. Put the hyphen at the end of the character class. — Wiktor Stribiżew, Jul 23 '16 at 11:54
Beside that unescaped dash, I suggest to consider to do the other way: match the desired tokens and return a list of all matches - you'll end up with a simpler regex: `return Regex.Matches(str, @"([()+*/-]|\d+)").Cast().Select(m => m.Value).ToArray();` — Dmitry Egorov, Jul 23 '16 at 12:07

score 1 · Answer 1 · answered Jul 23 '16 at 11:54

1

If it's just the 3-5 causing you problems, you need to escape the "-" in your pattern i.e.

Regex.Split(str, "(?<=[()\\-+*/])|(?=[()\\-+*/])")

answered Jul 23 '16 at 11:54

George Helyar

score 1 · Accepted Answer · answered Jul 23 '16 at 11:54

1

If you want to match a dash, it needs to be in the first or the last position in a character class in regex:

(?<=[()+*/-])|(?=[()+*/-])
//        ^            ^

Otherwise, it is interpreted as a character range - in your case, from ) to *.

answered Jul 23 '16 at 11:54

2 Answers2