Computer Programming Concepts and Visual Basic David I. Schneider

80 Computer Programming Concepts and Visual Basic
2. To obtain a list of the general procedures in a program, select (General) from
the Code window's Object box and then click on the down-arrow at the right
side of the Procedure box.
3. Sub procedures allow programmers to focus on the main flow of the program
and defer the details of implementation. Modern programs use them liberally.
An event procedure acts as a supervisor, delegating tasks to the Sub procedures.
This method of program construction is known as modular or top-down
design.
4. As a rule, a Sub procedure should perform only one task, or several closely
related tasks, and should be kept relatively small.
5. After a Sub procedure has been defined, Visual Basic automatically reminds
you of the Sub procedure’s parameters when you type in Call statements. As
soon as you type in the left parenthesis of a Call statement, a banner appears
giving the names and types of the parameters. The help feature is called Parameter
Info. See Figure 3-3.
FIGURE 3-3 The Parameter Info Help Feature
6. In this text, the first line inside a Sub procedure is often a comment statement
describing the task performed by the Sub procedure. If necessary, several comment
statements are devoted to this purpose. Conventional programming practice
also recommends that all variables used by the Sub procedure be listed in
comment statements with their meanings. In this text, we give several examples
of this practice but only adhere to it when the variables are especially numerous
or lack descriptive names.
7. Although both constants and expressions can be used as arguments in Call
statements, only variables can be used as parameters in Sub statements.
8. A Sub procedure can call another Sub procedure. If so, after the End Sub of the
called Sub procedure is reached, execution continues with the line in the calling
Sub procedure that follows the Call statement.
9. When you write a Sub procedure without parameters, Visual Basic automatically
adds a pair of empty parentheses at the end of the Sub procedure name.
However, Call statements should not use the empty parentheses.
10. The first lines of event procedures and Sub procedures end with a pair of parentheses.
With the event procedures we have discussed, the parentheses are usually
empty, whereas with Sub procedures, the parentheses often contain
parameters.
3.2 SUB PROCEDURES, PART II
The previous section introduced the concept of a Sub procedure but left some questions unanswered.
Why can’t the value of a variable be passed from an event procedure to a Sub proce-