Home > Articles

  • Print
  • + Share This
This chapter is from the book

Using Optional Arguments

You can make some arguments in a procedure call optional, which means that if the calling code doesn't specify a value for them, a default value will be used. To make an argument optional, you use the Optional keyword and supply a default value like this, where the strText argument of the ShowMessage function is optional and the default value is "Hello there!":

Module Module1

  Sub Main()

  End Sub

  Sub ShowMessage(Optional ByVal strText As String = "Hello there!")
    Console.WriteLine(strText)
  End Sub

End Module

Now if you call ShowMessage with no arguments, as shown in Listing 3.3 and the Optional project in the code for this book, the message "Hello there!" will be displayed.

Listing 3.3 Using Optional Arguments (Optional project, Module1.vb)

Module Module1

  Sub Main()
    ShowMessage()
    Console.WriteLine("Press Enter to continue...")
    Console.ReadLine()
  End Sub

  Sub ShowMessage(Optional ByVal strText As String = "Hello there!")
    Console.WriteLine(strText)
  End Sub

End Module

Note that if you declare one argument optional in a procedure's argument list, all following arguments must be optional too (otherwise, Visual Basic wouldn't know which argument had been omitted).

  • + Share This
  • 🔖 Save To Your Account