using System;

using System.Text.RegularExpressions;

​

public class Example

{

    public static void Main()

    {

        string pattern = @"(""|')((?!(?!\\)(\1|\n))|(\\(.|\n))|((?!\\).))*?(\1)";

        string input = @"""valid line""

​

'valid line 2'

​

''

​

""""

​

""'''""

""''''""

'""""""'

'""""""""'

​

""hello new line\

hello another line\

end blank line""

​

'hello blank line\

\ \\g\

end blank line'

​

""\'""

​

""\""""

​

""\""\

\\""

​

""invalid samples past this line""

​

""broken line

""

​

'broken line 

'

​

""broken line 2 \ffd

\hellod

""

'\'

""\""

​

'""

​

""'";

        var result = Regex.Matches(input, pattern);

        var count = 0;

        foreach (Match m in result)

        {

            if (m.Success)

            {

                Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);

                count++;

            }

        }

        Console.WriteLine(count);

    }

}

​