public static class GlobalMembers

{

    static int Main()

    {

    internal static class StringFunctions

    {

        public static string ChangeCharacter(string sourceString, int charIndex, char newChar)

        {

            return (charIndex > 0 ? sourceString.Substring(0, charIndex) : "") + newChar.ToString() + (charIndex < sourceString.Length - 1 ? sourceString.Substring(charIndex + 1) : "");

        }

​

        public static bool IsXDigit(char character)

        {

            if (char.IsDigit(character))

                return true;

            else if ("ABCDEFabcdef".IndexOf(character) > -1)

                return true;

            else

                return false;

        }

​

        public static string StrChr(string stringToSearch, char charToFind)

        {

            int index = stringToSearch.IndexOf(charToFind);

            if (index > -1)

                return stringToSearch.Substring(index);

            else

                return null;

        }

​

        public static string StrRChr(string stringToSearch, char charToFind)

        {

            int index = stringToSearch.LastIndexOf(charToFind);

            if (index > -1)

                return stringToSearch.Substring(index);

            else

                return null;

        }

​

        public static string StrStr(string stringToSearch, string stringToFind)

        {

            int index = stringToSearch.IndexOf(stringToFind);

            if (index > -1)

                return stringToSearch.Substring(index);

            else

                return null;

        }

​

        private static string activeString;

        private static int activePosition;

        public static string StrTok(string stringToTokenize, string delimiters)

        {

            if (stringToTokenize != null)

            {

                activeString = stringToTokenize;

                activePosition = -1;

            }

​

            if (activeString == null)

                return null;

            if (activePosition == activeString.Length)

                return null;

            activePosition++;

            while (activePosition < activeString.Length && delimiters.IndexOf(activeString[activePosition]) > -1)

            {

                activePosition++;

            }

​

            if (activePosition == activeString.Length)

                return null;

            int startingPosition = activePosition;

            do

            {

                activePosition++;

            }

            while (activePosition < activeString.Length && delimiters.IndexOf(activeString[activePosition]) == -1);

            return activeString.Substring(startingPosition, activePosition - startingPosition);

        }

    }

}