String format or REGEX

Question

I need an simple way to check whether a string that is sent to my function is of the form:

(x + n)(x + m) 
//the +'s can be minus'
//n and m represent a double
//x represents the char 'x'

Is there a simple string format that I can use to check that this is the form. As opposed to checking each character singularly.

The whitespace will be removed to save any confusion.

Regards

Lloyd

I'll bet his professor wouldn't accept regex as a solution, unless the lesson included regex. — Michael Meadows, Mar 16 '10 at 18:34
Regex was initially what I was looking at. But I was wondering if there was an easy way to check for '(' 'x' operator value')' consecutively. — Lloyd Powell, Mar 16 '10 at 18:38
Why do people just jump on the cocky remarks when certain questions are asked? I wanted to know for my own justification. Regex is the weakest of my programming tools and want to develop that area of my programming. Obviously asking here whilst you were about wasn't the best idea! — Lloyd Powell, Mar 16 '10 at 19:00

jessegavin · Accepted Answer · 2010-03-16T18:48:14.653

4

Here's a stab at a RegEx example...

var pattern = @"^(\(x[+-]\d+(\.\d+)?\)){2}$";
var input = "(x-0.123)(x+5)";
var result = System.Text.RegularExpressions.Regex.IsMatch(input, pattern);

if (result) { 
  Console.Write("YAY IT MATCHES");
}

edited Mar 16 '10 at 18:48

answered Mar 16 '10 at 18:41

jessegavin

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Thank you. I just can't seem to get my head around regex! Appreciated. – Lloyd Powell Mar 16 '10 at 18:43
Regex is super confusing. I use http://regexpal.com/ to play around with them until something works. They have a handy quick reference on the page. – jessegavin Mar 16 '10 at 18:46
Regular expressions are one of the more powerful items in your developer toolbox, but they can be a pain to learn using a compiled language. They really clicked for me in python because I could do things from the python interpreter and quickly try things out. – marr75 Mar 16 '10 at 18:53

score 2 · Answer 2 · answered Mar 16 '10 at 18:31

2

You can use regular expressions to check this.

answered Mar 16 '10 at 18:31

Andrew Bezzub

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Pratik Deoghare · Answer 3 · 2010-03-17T07:27:49.260

!Regex

Use this and you won't have 2 problems ;)

 class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(IsGood1("+x(3)-)x-5+"));
            Console.WriteLine(IsGood1("(x * n)(x + m)"));
            Console.WriteLine(IsGood1(" ( x + 12.9) (x+33.9)"));
        }

        private static bool IsOrdered(string s) // bad idea
        {
            var ind = new List<int>();
            ind.Add(s.IndexOf('('));
            ind.Add(s.IndexOfAny(new char[] { '+', '-' }));
            ind.Add(s.IndexOf(')'));
            ind.Add(s.LastIndexOf('('));
            ind.Add(s.LastIndexOfAny(new char[] { '+', '-' }));
            ind.Add(s.LastIndexOf(')'));

            bool order = true;

            for (int i = 0; i < ind.Count - 1; i++)
            {
                order = order && (ind[i] < ind[i + 1]);
            }
            return order;
        }

        public static bool IsGood1(string s)
        {
            if (!IsOrdered(s)) return false;

            double m = 0;
            int c = 0;

            foreach (var item in s.Split(new char[] { '+', '-', '(', ')' }))
            {
                var xx = item.Trim();

                if (xx != "")
                    switch (c)
                    {
                        case 0:
                        case 2:
                            if (xx == "x") c++;
                            break;
                        case 1:
                        case 3:
                            if (double.TryParse(xx, out m)) c++;
                            break;
                    }
            }

            return c == 4;
        }

    }

won't that accept `+x(3)-)x-5+` , and all other combination of `[-+()]`? — Kobi, Mar 16 '10 at 20:20
+1 Kobi Thanks! Took care of it but it looks dirty now! you know of some better way? Feel free to edit my answer :) — Pratik Deoghare, Mar 17 '10 at 07:28

score 1 · Answer 4 · edited May 23 '17 at 11:55

This is a case where I think Regular Expressions make a lot of sense. Unlike C++, C# does not have a way (that I know of) to use string formatting as part of parsing a string.

Quoting Eric Lippert:

Is this clever? No. Beautiful? No. Short? No. Correct according to the specification?

I hope so, but I have not fully tested it. ~~It looks pretty good though.~~

    static bool testJoin(string x)
    {
        string[] s = x.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
        if (s.Length != 3) return false;
        if (s[1] != "+" && s[1] != "-") return false;
        if (s[0] != "x") return false;
        double tmp;
        return Double.TryParse(s[2], out tmp);
    }
    static bool testString(string x)
    {
        if (x.Length < 2) return false;
        if (x[0] != '(' || x[x.Length-1]!=')') return false;
        string[] y = x.Substring(1,x.Length-2).Split(new string[] { ")(" }, StringSplitOptions.None);
        if (y.Length != 2) return false;
        return testJoin(y[0]) && testJoin(y[1]);
    }

Note that our specifications might not agree. For example, I require there to be one or more spaces before and after the +/-. — Brian, Mar 16 '10 at 18:57
For those who didn't get it, my reference to Eric Lippert was a joke, since his context was, "let's do it right, even if it isn't pretty" and my context is, "this isn't pretty." — Brian, Mar 16 '10 at 20:49

String format or REGEX

4 Answers4