Microsoft 9GD00001 manual VB MessagePrinter.vb

Chapter 3: Learning Just Enough C# and VB.NET: Types and Members 77

VB (MessagePrinter.vb):

Public Class MessagePrinter

Sub PrintCustomerReport(ByVal customers As String(), ByVal title

As String)

Console.WriteLine(title)

Console.WriteLine()

For Each name In customers

Console.WriteLine(name)

Next

End Sub

End Class

Parameters are a comma-separated list of identifiers, along with the type of each identifier, which clearly indicates what type of parameter the method is expecting. In Listing 3-6, the PrintCustomerReport method has two parameters: title of type string and customers of type string array. The method displays the title in the console window when you run the program, displays a blank line, and then iterates through the list, displaying each customer name to the console.

You can see how the Main method creates a new instance of MessagePrinter, which msgPrint points to, and then calls PrintCustomerReport using msgPrint. The arguments being passed, reportTitle and customerNames, match the position and types of the parameters for PrintCustomerReport, which are of the correct types that the PrintCustomerReport method is expecting.

In the preceding example, the calling code must provide arguments, actual data, for all parameters. However, you can specify parameters as being optional, allowing you to omit arguments for the optional parameters if you like. Here’s a modification to PrintCustomerReport where the title becomes an optional parameter:

C#:

public void PrintCustomerReport(

string[] customers, string title = "Customer Report")

{

Console.WriteLine(title);

Console.WriteLine();

foreach (var name in customers)

{

Console.WriteLine(name);

}

}