When the compiler sees that the MessageBox class is being used, it first looks in the global namespace , which is where all types end up that aren't contained by a namespace (for example, the MyFirstApp class is in the global namespace). If the compiler can't find the type in the global namespace, it looks at all the namespaces currently being used—in this case, System and System.Windows.Forms. If the compiler finds a type name being used that exists in two or more namespaces, it produces an error and we're forced to go back to the long notation. But in practice this is rare enough to make the short form the form of choice when you're typing code by hand. However, even though the MessageBox class is enormously handy for showing your users simple string information or asking them yes/no questions, it's hard to build a real application with MessageBox. For most things, you'll need an instance of the Form class (or a Formderived class):

Although this code will show the form, you'll have to be quick to see it because Show shows the form modelessly. If you're not steeped in user interface lore, a modeless form is one that displays but allows other activities (called modes ) to take place. So, immediately after Show puts our new form on the screen, it returns control to the Main function, which promptly returns, exiting the process and taking our nascent form with it. To show a form modally— that is, to not return control to the Main function until the form has closed—the documentation suggests using the ShowDialog function:

 

This code would show a blank form and wait for the user to close it before returning control to the Main function, but it's not the code you will generally be writing. Instead, to make it accessible in other parts of your application, you'll be designating one form as the main form. To do this, pass the main form as an argument to the Run method of the Application object, which also resides in the System.Windows.Forms namespace:

The Application class's static Run method will show the main form, and when it's closed, Run will return, letting our Main function exit and closing the process. To see this in action, you can compile your first WinForms application using the following command line