Page 51 - Excel for Scientists and Engineers: Numerical Methods

28 EXCEL: NUMERICAL METHODS

The Variant Data Type
The Variant data type is the default data type in VBA. Like Excel itself, the
Variant data type handles and interconverts between many different kinds of
data: integer, floating point, string, etc. The Variant data type automatically
chooses the most compact representation. But if your procedure deals with only
one kind of data, it will be more efficient and usually faster to declare the
variables as, for example, Integer.

Subroutines

By "subroutine" we mean a Sub procedure that is kalled" by another VBA
program. In writing a VBA procedure, it may be necessary to repeat the same
instructions several times within the procedure. Instead of repeating the same
lines of code over and over in your procedure, you can place this code in a
separate Sub program; this subroutine or subprogram is then executed by the
main program each time it is required.
There are several ways to execute a subroutine within a main program. The
two most common are by using the Call command, or by using the name of the
subroutine. These are illustrated in Figure 2-1 1. Mainprogram calls subroutines
Taskl and Task2, each of which requires arguments that are passed from the
main program to the subroutine and/or are returned from the subroutine to the
main program.

Sub Mainprogram()
etc.
Call Taskl (argument1 ,argument2)
e tc
Task2 argurnent3,argurnent4
efc
End Sub

Sub Taskl (ArgNamel ,ArgName2)
efc
End Sub

Sub Task2(ArgName3,ArgName4)
etc
End Sub
Figure 2-11. A main program illustrating the different syntax of subroutine calls.
The two methods use different syntax if the subroutine requires arguments.
If the Call command is used, the arguments must be enclosed in parentheses. If
only the subroutine name is used, the parentheses must be omitted. Note that the