using System;

public class Program

{

    public static void p (string c) {

        Console.WriteLine(c);

    }

    public static void Main()

    {

        v1();

        v2();

    }

    public static void v1()

    {

        string CandidateFirstName = "TestFirstName"; 

        string CandidateLastName = "TestLastName";

        string FromDisplayName = "firstname             lastname";

        //string FromDisplayName = null; 

        var fromDisplayNameSeparatorIndex = string.IsNullOrWhiteSpace(FromDisplayName) ? null : (int?)FromDisplayName.IndexOf(' ');

        p(fromDisplayNameSeparatorIndex.ToString()); 

        var CreateUserFirstName = fromDisplayNameSeparatorIndex.HasValue ? 

            fromDisplayNameSeparatorIndex.Value < 0 ? FromDisplayName : FromDisplayName.Substring(0, fromDisplayNameSeparatorIndex.Value)

                : CandidateFirstName;

        p(FromDisplayName.Substring(0, fromDisplayNameSeparatorIndex.Value)); 

        var CreateUserLastName = fromDisplayNameSeparatorIndex.HasValue ? 

            fromDisplayNameSeparatorIndex.Value < 0 ? string.Empty : FromDisplayName.Substring(fromDisplayNameSeparatorIndex.Value)

                : CandidateLastName;

        p(FromDisplayName.Substring(fromDisplayNameSeparatorIndex.Value)); 

​

    }

    public static void v2()

    {

        p("\nrefactoring");

        var CandidateFirstName = "TestFirstName"; 

        var CandidateLastName = "TestLastName";

        // string fromDisplayName = null;

        string fromDisplayName = "firstname             lastname";

        string[] splittedFullName  = fromDisplayName?.Split(" ", StringSplitOptions.RemoveEmptyEntries);

        p(splittedFullName.Length.ToString());

        var firstname = splittedFullName?[0] ?? CandidateFirstName;

        var lastname = splittedFullName?[1] ?? CandidateLastName;

        //p($"{firstname} {lastname}");

        p($"{firstname}");

        p($"{lastname}");

    }

}