C# :: Credit Card Validation - Not All Code Paths Return A Value

I have written the below but I get an error when I run it. I get the below error.

$mcs main.cs -out:demo.exe 2>&1

main.cs(93,58): warning CS0162: Unreachable code detected
main.cs(85,21): error CS0161: `CreditCards.CreditCardsValidator.LuhnCheckPerformed(string)': not all code paths return a value
Compilation failed: 1 error(s), 1 warnings

The code is below:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
/**@return a Credit Card Validation Application

[Code] ......