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Question

I am writing a program to check if a word is palindrome. The program itself works but when I enter this specific line of text "too bad - i hid a boot" it will not pick it up and ignore the white space and hyphen.

I looked at previous questions but I cant find a answer.

Is my Regex.Replace incorrect?

 string s, revs = "";
        Console.WriteLine("Please Enter Word");
        s = Console.ReadLine();
        string r = Regex.Replace(s , @"[^-\s]", "");

        for (int i = s.Length-1; i >= 0; i--)
        {
            revs += s[i].ToString();
        }

        if (revs == s)
        {
            Console.WriteLine("Entered string is palindrome \n String was {0} and reverse string was {1}", s, revs);
        }
        else
        {
            Console.WriteLine("String entered was not palindrome.");
        }
        Console.ReadKey();

Answer 1

Your code contains two errors:

• This is the correct Regex condition @"(\\s|-)" yours replaces everything but the characters you want to remove
• As jeffdot pointed out, you're replacing (incorrectly) but then testing against the original string

This considered, the correct code should be:

string s, revs = "";
        Console.WriteLine("Please Enter Word");
        s = Console.ReadLine();
        string r = Regex.Replace(s , @"(\s|-)", "");

        for (int i = r.Length-1; i >= 0; i--)
        {
            revs += r[i].ToString();
        }

        if (revs == r)
        {
            Console.WriteLine("Entered string is palindrome \n String was {0} and reverse string was {1}", s, revs);
        }
        else
        {
            Console.WriteLine("String entered was not palindrome.");
        }
        Console.ReadKey();

Except for the first WriteLine in which you should decide what to print (since revs doesn't contain spaces and the hyphen anymore).

Or if you want to just use String.Replace , you can use it twice with:

s=s.Replace(' ','');
s=s.Replace('-','');

Answer 2

You are assigning the result of that Regex.Replace call to string r and you are never referencing it. This is why your comparison is failing.

To make that more clear: you are removing whitespace and referencing that product as string r but you are reversing and testing against string s only.

Saverio also points out that your regex isn't going to work (I didn't test that myself).

You have:

    string r = Regex.Replace(s , @"[^-\s]", "");

    for (int i = s.Length-1; i >= 0; i--)
    {
        revs += s[i].ToString();
    }

Right there you should be iterating and reversing r instead of s --because s still has all its whitespace.

Further, as Saverio has said, why not just replace?

string r = s.Replace(" ", string.Empty).Reverse();

I haven't tried to compile that but as long as you are not using a very old version of the .NET framework that should work. It may require that you are using System.Linq to use the Reverse() extension.