C# Regular expression

c#, regex

Solution

The regular expression that will detect multiple powers is

(\d+\^){2,}

(`{2,}` means two or more times in a row)

Just ran the following Test:

using System;
using System.Text.RegularExpressions;
namespace SampleNamespace
{
    public class SampleClass
    {
        public static void Main()
        {
            string line = "1+3^4^5  10+3+4*5+2^5^6^7";              
            System.Console.WriteLine(line);
            line = Regex.Replace(line, @"(\d+\^){2,}", "0");
            System.Console.WriteLine(line);
        }
    }
}

Output was:

>RegexTest.exe
1+3^4^5  10+3+4*5+2^5^6^7
1+05  10+3+4*5+07

It failed to replace the trailing \d but it does work. You can grab the trailing \d with the following correction to the regex:

(\d+\^){2,}\d+

If you want to wipe out the entire expression that contains a double power just use

.*(\d+\^){2,}.*

in your replace expresion. The `.*` on either side will swallow up the entire string surrounding the double power when a replacement takes place.

Problem

I have plain text file (`.txt`) which has some expressions and I want to replace invalid expression with... ...let's say zero. An invalid expression is expression which contains `1+3^4^5` or `10+3+4*5+2^5^6^7`, i.e. an expression can't contain `number^number^number^...`, it can only contain `number^number`. I understand that best way to do this is to use Regex but I dont know how to write this in regex.

Original source