The Debug class

When debugging a program, it is sometimes handy to write intermediate output on the development system's Output debugging window. If the Output window is not visible, click View > Other Windows > Output.

Let us look at four methods of the debug class: WriteLine, Write, WriteLineIf, and WriteIf.

This example illustrates WriteLine: 

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim a As Integer
   For a = 1 To 5
      Debug.WriteLine(a + 10)
   Next
End Sub

Would not display any output on the form, but it would write: 

   11
   12
   13
   14
   15
in the development system's Debug window.

As you see, the program uses the WriteLine method of the Debug class. The arguments of the Writeline method can be a string, numeric or Boolean expression: 

Debug.Writeline (<expression>)

The Debug class also has a Write method, which writes output in the Debug window but does not include a carriage-return line feed.

Finally, there is the WritelineIf and WriteIf methods. These methods only write output if a boolean expression is true. The syntax is: 

Debug.WritelineIf (<Boolean expression>, <expression>)

For example, this program: 

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
   Dim a As Integer
   For a = 1 To 5
      Debug.WriteLineIf (a = 2, a + 10)
   Next
End Sub

only writes output when the variable a has a value of 2.

Note that if you use the Debug class, be sure you compile in debug mode (as opposed to release mode).