Programming with Microsoft Visual Basic 2010 5 th Edition

1. Programming with Microsoft Visual Basic 2010 5th Edition Chapter Seven Sub and Function Procedures

2. Previewing the Harvey Industries Application • Open the Harvey Industries.exe file • The Harvey Industries application calculates payroll for an employee

3. Previewing the Harvey Industries Application (cont’d.) Figure 7-1 Interface showing the payroll calculations

4. Lesson A Objectives After studying Lesson A, you should be able to: • Explain the difference between a Sub procedure and a Function procedure • Create a procedure that receives information passed to it • Explain the difference between passing data by value and passing data by reference • Create a Function procedure

5. More About Sub Procedures • Procedure • Block of program code that performs specific task • Two types of Sub procedures in Visual Basic • Event procedure • Procedure associated with specific object and event • Independent Sub procedure • Independent of any object and event • Processed only when called (invoked)

6. Passing Variables • Variables • Have both value and unique address • Passing by value • Passes a copy of the variable’s value • Example: Disclosing your bank account balance • Passing by reference • Passes a variable’s address • Example: Disclosing your bank account number

7. Passing Variables by Value • Provides only contents of variable to receiving procedure • How to pass by value: • Include keyword ByVal before parameter • Reasons to pass by value: • Procedure needs to know contents of variable • Procedure does not need to change original value • By default, Visual Basic passes by value

8. Example: Event and Sub Procedure

9. Figure 7-5 ShowMsg procedure and btnDisplay Click event procedure

10. Passing Variables by Reference • Provides address (memory location) of variable to procedure • Receiving procedure can thus access variable • Reason to pass by reference • Procedure needs to change variable’s contents • How to pass by reference • Include keyword ByRef before parameter

11. Example (Using Sub Procedures)

12. Figure 7-8 CalcGrossPay procedure and btnCalc control’s Click event procedure

13. Function Procedures • Function procedure • Block of code that performs specific task • Returns value after completing its task • Visual Basic provides built-in functions • Can also create your own functions • As datatype in header indicates return type of data • Returnexpression type must agree with As datatype

14. Figure 7-14 Function procedure syntax, examples, and steps

15. Function Procedures (cont’d.) Figure 7-15 Examples of invoking the GetNewPrice function

16. Example: Using Functions

17. Figure 7-16 CalcGrossPay function and btnCalc control’s Click event procedure

18. Lesson A Summary • Two types of Sub procedures • Event and independent • Function: Performs task and returns value • Independent procedures and functions • Called from application’s code using Call statement • Pass by value • Send copy of variable’s contents to procedure or function • Pass by reference • Send variable’s address to procedure or function

19. Lesson B Objectives After studying Lesson B, you should be able to: • Include a combo box in an interface • Add items to a combo box • Select a combo box item from code • Determine the item either selected or entered in a combo box • Code a combo box’s TextChanged event procedure

20. Including a Combo Box in an Interface • Combo box • Allows user to select from number of choices • Allows user to type entry not on list • Can save space on form • List box does not share features two and three • DropDownStyle property • Values: Simple, DropDown (default), DropDownList

21. Including a Combo Box in an Interface (cont’d.) Figure 7-19 Examples of the combo box styles

22. Figure 7-20 Code associated with the combo boxes in Figure 7-19

23. Including a Combo Box in an Interface (cont’d.) • To process code when Text property changes • Use TextChanged event procedure • Use Item collection’s Add method to add item • Other properties of combo box • Sorted: Sorts items in dictionary order • SelectedIndex: Used to select item in list portion • SelectedItem: Contains value of item selected • Text: Contains value that appears in text portion • Use label control to provide keyboard access to the combo box

24. Including a Combo Box in an Interface (cont’d.) Figure 7-22 Gross pay amount shown in the interface

25. Lesson B Summary • Use ComboBox tool to add combo box to form • Specify style of combo box using DropDownStyle property • Use Items collection’s Add method to add items to Combo box • Use combo box’s Sorted property to sort items in combo’s list • Enter code in combo box’s TextChanged event procedure • To process code when Text property changes

26. Lesson B Summary (cont’d.) • Use SelectedIndex, SelectedItem, or Text property: • To select combo box item from code • To determine item that was selected

27. Lesson C Objectives After studying Lesson C, you should be able to: • Prevent a form from closing • Round a number

28. Creating the Harvey Industries Application • Application objective is to calculate: • Employee’s weekly gross pay • Federal withholding tax (FWT) • Social Security and Medicare (FICA) tax • Net pay • Review TOE chart for requirements

29. Coding the Harvey Industries Application (cont’d.) Figure 7-26 User interface for the Harvey Industries application

30. Coding the FormClosing Event Procedure • FormClosing event • Occurs when form is about to be closed because: • Computer processes Me.Close() statement • User clicks Close button on form’s title bar • Requirement for FormClosing event procedure • Verifying that user wants to close application • Taking appropriate action based on user’s response • To prevent closing • Set Cancelproperty of FormClosing procedure’s e parameter to true

31. Coding the FormClosing Event Procedure (cont’d.) Figure 7-27 Pseudocode for the FormClosing event procedure

32. Coding the FormClosing Event Procedure (cont’d.) Figure 7-28 Message box displayed by the code in the FormClosing event procedure

33. Coding the btnCalc Control’s Click Event Procedure Figure 7-29 Pseudocode for the btnCalc control’s Click event procedure

34. Coding the btnCalc Control’s Click Event Procedure (cont’d.) Figure 7-30 Selection structure entered in the procedure

35. Creating the GetFwt Function • How to calculate weekly taxable wages • Multiply number of withholding allowances by $70.19 • Subtract this result from weekly gross pay • Determining federal withholding tax (FWT) • Evaluate weekly taxable wages and filing status • Use data to look up FWT in special FWT tables • GetFwt function emulates FWT table lookup

36. Creating the GetFwt Function (cont’d.) Figure 7-33 FWT calculations for a married taxpayer whose weekly taxable wages are $388.46

37. Creating the GetFwt Function (cont’d.) Figure 7-34 FWT calculations for a single taxpayer whose weekly taxable wages are $600

38. Creating the GetFwt Function (cont’d.) Figure 7-35 Pseudocode for the GetFwt function

39. Creating the GetFwt Function (cont’d.) Figure 7-36 GetFwt function header and footer

40. Completing the btnCalc Control’s Click Event Procedure • Must call GetFwt function from btnCalc’s Click event procedure • Math.Round function • Round value to specific number of decimal places • Syntax: Math.Round (value[, digits]) • value: Numeric expression to work on • digits: Integer indicating number of places to right of decimal point

41. Completing the btnCalc Control’s Click Event Procedure (cont’d.) Figure 7-37 Payroll calculations displayed in the interface

42. Lesson C Summary • Use form’s FormClosing event procedure to process code when form is about to be closed • Set Cancel property of FormClosing event procedure’s e parameter to true to prevent form from being closed • Use Math.Round function to round number to specific number of decimal places