Question

This is the input string “23x +y-34 x + y+21x – 3y2-3x-y+2”. I want to surround every ‘+’ and ‘-‘ character with whitespaces but only if they are not allready sourrounded from left or right side. So my input string would look like this “23x + y – 34 x + y + 21x – 3y2 – 3x – y + 2”. I wrote this code that does the job:

    Regex reg1 = new Regex(@"\+(?! )|\-(?! )");
    input = reg1.Replace(input, delegate(Match m) { return m.Value + " "; });
    Regex reg2 = new Regex(@"(?<! )\+|(?<! )\-");
    input = reg2.Replace(input, delegate(Match m) { return " " + m.Value; });

explanation:
reg1 // Match ‘+’ followed by any character not ‘ ‘ (whitespace) or same thing for ‘-‘

reg2 // Same thing only that I match ‘+’ or ‘-‘ not preceding by ‘ ‘(whitespace)

delegate 1 and 2 just insert ” ” before and after m.Value ( match value )

Question is, is there a way to create just one regex and just one delegate? i.e. do this job in one step? I am a new to regex and I want to learn efficient way.

Answer 1

I don’t see the need of lookarounds or delegates here. Just replace

\s*([-+])\s*

with

" $1 "

(See http://ideone.com/r3Oog.)