Computer Programming Concepts and Visual Basic David I. Schneider

3.1 SUB PROCEDURES, PART I
Structured program design requires that problems be broken into small problems to be solved
one at a time. Visual Basic has two devices, Sub procedures and Function procedures, that
are used to break problems into manageable chunks. To distinguish them from event procedures,
Sub and Function procedures are referred to as general procedures. General procedures also
eliminate repetitive code, can be reused in other programs, and allow a team of programmers
to work on a single program.
In this section we show how Sub procedures are defined and used. The programs in this
section are designed to demonstrate the use of Sub procedures rather than to accomplish
sophisticated programming tasks. Later chapters of the book use them for more substantial
programming efforts.
A Sub procedure is a part of a program that performs one or more related tasks, has its
own name, is written as a separate part of the program. The simplest type of Sub procedure
has the form
Private Sub ProcedureName()
statement(s)
End Sub
A Sub procedure is invoked with a statement of the form
Call ProcedureName
The rules for naming general procedures are identical to the rules for naming variables.
The name chosen for a Sub procedure should describe the task it performs. Sub procedures
can be either typed directly into the code window, or into a template created with the following
steps:
1. Press Alt/T/P to select Add Procedure from the Tools menu.
2. Type in the name of the procedure. (Omit parentheses.)
3. Select Sub from the Type box.
4. Select Private from the Scope box. Note: Actually either Public or Private is
OK. A Public procedure is available to all forms, whereas a Private procedure
is only available to the form in which it is defined.
5. Press the Enter key or click on OK.
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