CS0246_Error.htm
 // Hello_world
//using System;
//compile csc test2.cs
class test2
{
public static void Main()
{
Console.WriteLine("Hello World");

}
} 		// Hello_world
using System;
//compile helloworld.cs
class test2
{
public static void Main()
{
Console.WriteLine("Hello World");

}
}
Meaning your file was not found.
 

Now real programming glitch

 

Let us fix it

// Hello_world
using System;
//compile helloworld.cs
class test2
{
public static void Main()
{
Console.WriteLine("Hello World");

}
}

 
 // Hello_world blaba baaljasfsdfdsjf
using System;
//compile helloworld.cs
class test2
{
public static void Main()
{
Console.WriteLine("Hello World");
// your program will wait for you
Console.ReadLine();
}
}