In this post we provide the C# source code for a very simple example of a class library, as we continue from the previous post.

Here is where you can store all of your library routines. Our example only has three objects: a welcome string, a time two method, and a times three method. For a client application to use these they must be public. Also, static objects do not need to be instantiated by the calling application.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using static System.Console;

namespace ClassLibrary
{
    public class ExternalClass
    {
        public string strWelcomeMsg = "Welcome!";

        public long TwoTimesInt(int intMyInteger)
        {
            return (2 * intMyInteger);
        }
        public static long ThreeTimesInt(int intMyInteger)
        {  // static does not need to be instantiated.
            return (3 * intMyInteger);
        }
    }
}

Here is what the Solution Explorer looks like. There is an internal class but there is no code in it.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using static System.Console;
using ClassLibrary;  // this is my class

namespace ClientApp
{
    class Program
    {
        static void Main(string[] args)
        {
            // This app makes use of my C# ClassLibrary
            // I needed to add a reference to my library
            // Optionally I can add a using statement as shown above.
            long longResult;
            longResult = ExternalClass.ThreeTimesInt(3);
            WriteLine(longResult);
            ClassLibrary.ExternalClass myObj = new ClassLibrary.ExternalClass();
            longResult = myObj.TwoTimesInt(3);
            WriteLine(longResult);
            WriteLine(myObj.strWelcomeMsg);
            ReadKey();
        }
    }
}

Here is a view of the Solution Explorer for the client application.

Here is a view of the Object Browser for the client application.

Making use of external classes in external assemblies is necessary in C# programming and is something you do all the time when you use any of the classes in the .NET Framework.