Clearly Visual Basic: Programming with Visual Basic 2010 2 nd Edition

1. Clearly Visual Basic: Programming with Visual Basic 2010 2nd Edition Chapter 16 I Hear You Are Breaking Up (Sub Procedures)

2. Objectives After studying Chapter 16, you should be able to: • Create a Sub procedure • Call a Sub procedure • Pass data by value to a procedure • Pass data by reference to a procedure Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

3. What’s the Proper Procedure? • Sub procedures • Blocks of code that perform a specific task • Allow large and complex applications to be broken into small and manageable tasks • You can use a Sub procedure to: • Avoid duplicating code in different parts of a program • Keep an event procedure’s code from getting unwieldy and difficult to understand Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

4. What’s the Proper Procedure? (cont.) What’s the Proper Procedure? (cont’d.) Figure 16-1 Sample Click event procedure for an Exit button Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

5. What’s the Proper Procedure? (cont’d.) • Independent Sub procedure • Independent of any object and event • Has a procedure header and a procedure footer • Figure 16-2 • Shows syntax for creating an independent Sub procedure in Visual Basic Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

6. Figure 16-2 Syntax, example, and steps for creating an independent Sub procedure Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

7. What’s the Proper Procedure? (cont’d.) • Convention for naming a Sub procedure • Enter procedure names using Pascal case • Common practice to begin a procedure’s name with a verb • Parameters • Store the information passed to the procedure when it is invoked Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

8. What’s the Proper Procedure? (cont’d.) • Call statement • Used to invoke a Sub procedure • procedureName • Name of the procedure you are calling (invoking) • argumentList • Comma-separated list of arguments • Argument • Represents information passed to the procedure when it is invoked Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

9. What’s the Proper Procedure? (cont’d.) Figure 16-3 Syntax and an example of the Call statement Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

10. The Weekly Pay Application • The application • Calculates and displays an employee’s regular pay, overtime pay, and gross pay • A text box’s TextChanged event • Occurs whenever a change is made to the contents of the text box Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

11. Send Me Something • Number of arguments • Call statement should agree with the number of parameters in the procedure header • Passing by value • Passing a variable’s value • Passing by reference • Passing a variable’s address Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

12. Just Give Me Its Value • To pass a variable by value in Visual Basic: • Include the keyword ByVal before the variable’s corresponding parameter in the receiving procedure’s parameterList • When you pass a variable by value: • Computer passes a copy of the variable’s contents to the procedure • You pass a variable by value when: • Receiving procedure needs to know variable’s contents but does not need to change the contents Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

13. Where Do You Live? • You pass a variable by reference: • When you want the receiving procedure to change the contents of the variable • To pass a variable by reference: • Include the keyword ByRef before the variable’s corresponding parameter in the receiving procedure’s parameterList Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

14. Where Do You Live? (cont’d.) Figure 16-13 Interface for the Total Due Calculator application Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

15. Figure 16-14 Planning information for the Total Due Calculator application Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

16. Summary • Sub procedures • Allow you to avoid duplicating code in different parts of a program • Common practice • To begin a procedure name with a verb and to enter the name using Pascal case • Call statement • Used to invoke an independent Sub procedure Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition

17. Summary (cont’d.) • When calling a procedure: • The number of arguments listed in the Call statement’s argumentList should agree with the number of parameters listed in the receiving procedure’s parameterList • Passing information • By reference • By value Clearly Visual Basic: Programming with Visual Basic 2010, 2nd Edition