Question

I am looking for a regular expression in C# to match any of these strings: “+99.99”, “-99.99”, “99.99”. The same regular expression should not match the string “+-99.99”. Can any one please suggest an answer.

Answer 1

The following worked for me:

        String regex = "^(\\+|-)?99\\.99$";
        String str1 = "-99.99";
        String str2 = "+99.99";
        String str3 = "99.99";
        String str4 = "+-99.99";

        System.Console.WriteLine(Regex.IsMatch(str1, regex));
        System.Console.WriteLine(Regex.IsMatch(str2, regex));
        System.Console.WriteLine(Regex.IsMatch(str3, regex));
        System.Console.WriteLine(Regex.IsMatch(str4, regex));

        System.Console.ReadKey();

Yielded:

True True True False

Explanation: ^ will instruct the regex engine to start matching from the beginning of the string, (\\+|-) denotes a + or - character. The + is a special character in regex syntax and thus needs to be escaped. The OR operator is denoted by the | character.

The ? denotes that the + or - character may or may not be there (it will match 0 or 1 instances of whatever preceeds it).

99\\.99 denotes the string 99.99. The . is also a special character in regex syntax and thus needs to be escaped. The $ character will instruct the regex engine to stop matching at the end of the string.