I have learned how to make DLL file from the link:
http://www.c-sharpcorner.com/UploadF...058AM/dll.aspx
but when i build my file the error comes:
A project with an output type of class library cannot be started directly.

In order to debug this project, add an executable project to this solution which references the library project. Set the executable project as the startup project.

What should i do to remove this error, i m just a novice, plz tell me step by step. Thank u in advance.

How to do programming?

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How to do programming?

Just do exactly what the message tells you.

A DLL is only a LIBRARY. It is designed to be something that is CALLED by other pieces of code.

So the message is telling you that you must create another project--this time one that is NOT a DLL project--and then you can call the routines in your library (your DLL) from that project.

Suppose, for example, that your DLL contains a class named "MyClass" and that class has a method called "MyMethod".

Okay, then you would create an executable program (a ".exe" or equivalent) that would do
    MyClass myObject = new MyClass( );
    myObject.MyMethod( );
or however you designed the class that is in your library.

Again, read the error message. It is telling you everything you need to do:

In order to debug this project, add an executable project to this solution which references the library project. Set the executable project as the startup project.

How to do it? how to create exe file plz tell me step by step

I have a better idea.

Start over learning C#.

You should have created an executable a *LONG* time before you even began thinking about creating a DLL.

Go to http://www.asp.net/Learn or to http://msdn.microsoft.com/Express and work your way through one or more of the "startup" tutorials on programming in C#.

In the long run, this will save you a lot of time and trouble and problems.