C# Online Compiler | .NET Fiddle

using System;

using System.Linq;

namespace ConsoleApplication1
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string[] delhiResidents = { "Ramesh", "Kapil", "Vikas", "Amit" };
            string[] kolkataResidents = { "Kapil", "Manmohan", "Deepak", "Amit" };

            var allResidents = delhiResidents.Union(kolkataResidents);

            foreach (var item in allResidents)
            {
                Console.WriteLine(item);
            }
        }
    }
}

 
using System;
​
using System.Linq;
​
namespace ConsoleApplication1
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string[] delhiResidents = { "Ramesh", "Kapil", "Vikas", "Amit" };
            string[] kolkataResidents = { "Kapil", "Manmohan", "Deepak", "Amit" };
​
            var allResidents = delhiResidents.Union(kolkataResidents);
​
            foreach (var item in allResidents)
            {
                Console.WriteLine(item);
            }
        }
    }
}

Unhandled exception. System.TypeInitializationException: The type initializer for 'System.Data.Entity.DbContext' threw an exception.
---> System.TypeInitializationException: The type initializer for 'Z.EntityFramework.Classic.EntityFrameworkManager' threw an exception.
---> System.TypeInitializationException: The type initializer for '' threw an exception.
---> System.IO.FileNotFoundException: Could not load file or assembly 'System.Configuration.ConfigurationManager, Version=8.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'. The system cannot find the file specified.

File name: 'System.Configuration.ConfigurationManager, Version=8.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'
   at Z.Expressions.CompilerManager..cctor()
   at Z.Expressions.CompilerManager.LoadEntityFrameworkClassicConfiguration()
   at Z.Expressions.ExceptionMessage.ThrowLicenseException()
   at ..cctor()
   --- End of inner exception stack trace ---
   at .()
   at Z.EntityFramework.Classic.EntityFrameworkManager..cctor()
   --- End of inner exception stack trace ---
   at Z.EntityFramework.Classic.EntityFrameworkManager.Initialize()
   at System.Data.Entity.DbContext..cctor()
   --- End of inner exception stack trace ---
   at System.Data.Entity.DbContext..ctor(String nameOrConnectionString)
   at Program.EntityContext..ctor()
   at Program.Main()
Command terminated by signal 6