Matakuliah
Tahun
: T0063 – Pemrograman Visual
: 2009
Reducing Program Complexity
General Sub Procedures and Developerdefined Functions
CHAPTER SIX
Introduction
• Three important consideration help us design, construct,
and maintain complex programs:
1. Break complex tasks into smaller “subtasks.”
2. Give each subtask a descriptive name.
3. Find processing tasks that have subtasks in common.
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Objectives
• Share code by creating general sub procedures and
functions.
• Use parameters to share data between procedures and
functions.
• Use code modules to organize code for reusability.
• Use the KeyPress, Enter, and Leave events.
• Use the concept of form modality.
• Create and program main menus.
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6.1 General Sub Procedures
• We must be very precise in writing the criterion and
alternative actions for decisions.
• In a program,
– A condition is represented as an expression.
– An outcome is the result of an evaluated condition.
– An appropriate action follows the outcome.
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6.1 General Sub Procedures (cont.)
• Execution of General Sub Procedures
– Names of event procedures always end with an
underscore followed by the type of event.
– Names of general sub procedures do not.
– A procedure call invokes a procedure.
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6.1 General Sub Procedures (cont.)
• Local Variables in General Sub Procedures
– General sub procedures can access module-level and
global variables.
– They have their own variables.
– Procedure-level variables are not related to other
procedures.
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6.1 General Sub Procedures (cont.)
• General Sub Procedures and Project Structure
– Locating a General Sub Procedure in the Code
Window
• We enter and view event procedures in the Code
window.
• We also enter and view general sub procedures in
the Code window.
• Scroll to find a procedure’s heading.
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6.1 General Sub Procedures (cont.)
• Creating General Sub Procedures
– Start from the Code window of a form or code module.
– Enter header for the sub procedure.
– Enter general sub procedure statements.
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6.2 Procedures with Parameters (cont.)
• Parameter Passing
– Sending data from the calling to the called procedure.
– Parameter Lists
• List of data items a procedure expects any calling
procedure to send it.
– Procedure Calls with Parameters
• See Figure 6.16 in textbook.
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6.2 Procedures with Parameters (cont.)
• Multiple Parameters
– A parameter list is key.
– Every parameter list should contain:
• Number of arguments.
• Types of arguments.
• Sequence of arguments.
• Names arguments are referred to.
• What the parameters and arguments represents?
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6.2 Procedures with Parameters (cont.)
• Passing Expressions
– Calling procedure can pass an expression.
• Correcting Common Mistakes in Parameter Passing
– Arguments Not Specified
• Number of arguments must match parameters.
– Invalid Cast Exception
• Parameter and argument type mismatch.
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6.2 Procedures with Parameters (cont.)
– Arguments Out of Order
• Arguments and parameters must be associated by
position, not by name.
– Conflict between Parameter Name and Local Variable
Name
• Parameter name and local variable names must be
different.
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6.2 Procedures with Parameters (cont.)
• General Sub Procedures versus Event Procedures
– An event procedure is always associated with a
control.
– Developers create the procedure heading for a
general sub procedure.
– Visual Basic .NET creates the procedure heading for
an event procedure.
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6.2 Procedures with Parameters (cont.)
• General Sub Procedures versus Event Procedures and
the Object Paradigm
– We have created a form class.
– We also created two methods.
• One was event procedure.
• The other was a general sub procedure.
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6.3 Developer-Defined Functions
•
•
•
•
Perform calculations or string manipulations.
Return values.
Use Return statements.
Function headings include type specifications.
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6.3 Developer-Defined Functions (cont.)
• Creating Functions
– Follow the same steps to create a general sub
procedure.
– Use the keyword Function instead of Sub.
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6.4 Code Modules
• Sub Main
– Use to begin execution of the program by executing a
general sub procedure.
– Select in the Misc Property Pages dialog box under
the Project menu.
– You must create a public general sub procedure
named Main in a code module.
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6.4 Code Modules (cont.)
• Libraries
– Programmers organize reusable code for easy
access.
– A collection of code modules in categories is called a
library.
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6.5 The MainMenu Control
• Start by right-clicking on the MainMenu control in the
component tray.
• Then select Edit Menu from the pop-up menu.
• Enter both main and sub menu items.
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