Page 46 - Excel for Scientists and Engineers: Numerical Methods

CHAPTER 2 FUNDAMENTALS OF PROGRAMMING WITH VBA 23

Other Keywords
In addition to VBA's objects, properties, methods and functions, there are
additional keywords that deal with program control: looping, branching and so
on. These keywords are described in detail in the following sections.
VBA keywords that will not be discussed in this book include objects such
as menu bars, menus and menu commands, toolbars and toolbuttons and the
many properties and methods pertaining to them.

Program Control

If you are familiar with computer languages such as BASIC or FORTRAN,
you will find yourself quite comfortable with most of the material in this section.

Branching
VBA supports If ... Then statements very similar to the Excel worksheet
function IF. The syntax of If ... Then is

If LogicaExpression Then statement? Else statement2
The If ... Then statement can be a Simple If statement, for example:
If (x PO) Then numerator = 10 ,-, x

If LogicaExpression (in this example x > 0) is True, statement? is carried
out; if LogicaExpression is False, nothing is done (program execution moves to
the next line).
If ... Then. ..Else structures are also possible. For example:

If Err.Number = 13 Then Resume ptl Else End
In a Block If statement, If LogicaExpression Then is followed by multiple
statement lines and is terminated by End If, as in Figure 2-1.
If Err.Number = 13 Then
On Error GoTo 0 'Disable the error handler.
Resume ptl 'and continue execution.
End If
Figure 2-1. Example of VBA Block If structure.

You can also create a Block-If-type structure in a single line, as in the
following statement.

If LogicaExpfession Then statement? : statement2 Else statement3
If ... Then ... Elself structures are also possible, as illustrated in Figure 2-2.