C# Regex.Split() does not work as expected

Question

I'm trying out services in C#, so I cannot debug values using Console.WriteLine(...). That's why I don't know what is in my variable number at the end:

    public int addAndSoustractNumberFromAString(string ustr)
    {
        int result = 0;

        if(!string.IsNullOrEmpty(str))
        {
            string str = ustr.Trim();

            //Regexes
            System.Text.RegularExpressions.Regex valid_regex = new System.Text.RegularExpressions.Regex(@"[\+]\d+|[\-]\d+");
            System.Text.RegularExpressions.Regex invalid_regex = new System.Text.RegularExpressions.Regex(@"[a-zA-Z]");

            //Handling errors
            if (invalid_regex.IsMatch(str) || !valid_regex.IsMatch(str) || !Char.IsDigit(str[str.Length - 1])) return 0;
            if (Char.IsDigit(str[0])) str = "+" + str;

            //Load all numbers in a string array
            List<string> numbers = new List<string>(valid_regex.Split(str).ToArray());

            //Cast string numbers to int + result calculation
            foreach (string number in numbers) { if (!int.TryParse(number, out int n)) return 99; result += n; }
        }

        return result;
    }

What does my code? I enter additions & subtractions, it does the operations & return the result as an integer.

example: If I enter "52-2+3" it should return 53

Problem: My code always returns 99 which means the parsing failed. Just in case, I tried int.TryParse("-2", out int n) instead and it works fine.

The line that is not working:

List<string> numbers = new List<string>(valid_regex.Split(str).ToArray());

My regexes are fine, I tested them with the website regexstorm net.

My question is, why my string isn't split correctly using a supposed valid regex? Is Regex.Split() not doing what I believe it does? (I thought it would split my string into +number or -number strings

Side note: it's ok if it does not start with a sign. If my string starts with a number it will add "+" at the end for regex purposes.

Why do you declare an int inside the call to TryParse ? Don't you want to get this value ? Have you tried declaring int n; then int.TryParse(number, out n) ? — Rafalon
– Rafalon, Commented Jul 7, 2017 at 15:12
Yeah, it works for my other methodes. Just in case I tested and it still shows 99. It's ok to declare it inside the function TryParse. — Sanchez Tanguy
– Sanchez Tanguy, Commented Jul 7, 2017 at 15:16
Couldn't you get this code into a Console Application and debug it there? — Dan Dumitru
– Dan Dumitru, Commented Jul 7, 2017 at 15:18
People are serious downvoting without saying anything... I tested a lot of things before posting it here... :/ No I can't, it use ISS, Console.WriteLine(...) doesn't work. — Sanchez Tanguy
– Sanchez Tanguy, Commented Jul 7, 2017 at 15:18
This is probably simpler: Wrapping a C# service in a console app to debug it — Alex K.
– Alex K., Commented Jul 7, 2017 at 15:21

Mark Peters · Accepted Answer · 2017-07-07 16:36:46Z

1

Your Regex is not a Split()ing Regex.

Split() expects the regular expression to define the delimiter (i.e. split on a comma or semicolon). Your regex describes the values.

It seems like you want the result of Matches() and not Split().

This seems to work for me with your example:

List<string> numbers = valid_regex.Matches(str).Cast<Match>().Select(m => m.Value).ToList();

Also, LinqPad is a wonderful tool to prototype code snippets like this one.

edited Jul 7, 2017 at 16:36

answered Jul 7, 2017 at 15:22

Mark Peters

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1 Comment

Sanchez Tanguy Over a year ago

It's working ! So as expected I was misunderstanding the regex.split() function. Thanks !

Rafalon · Accepted Answer · 2017-07-07 15:37:34Z

0

Replacing your regexp with ([\+\-]\d+) made the trick with the example "52-2+3" here.

Also added .Where(x => !String.IsNullOrEmpty(x)).ToList(); after the split so you get rid of empty strings.

edited Jul 7, 2017 at 15:37

answered Jul 7, 2017 at 15:30

Rafalon

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