Programming with Microsoft Visual Basic 2008 Fourth Edition

1. Programming with Microsoft Visual Basic 2008 Fourth 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 2 Programming with Microsoft Visual Basic 2008, Fourth Edition

3. Previewing the Harvey Industries Application (continued) 3 Programming with Microsoft Visual Basic 2008, Fourth Edition

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 4 Programming with Microsoft Visual Basic 2008, Fourth Edition

5. Procedures Procedure: Block of program code that performs specific task Two types of procedures in Visual Basic: Sub procedure: Does not return value Function procedure: Does return value Programming with Microsoft Visual Basic 2008, Fourth Edition 5

6. Sub Procedures Two types of Sub procedures in Visual Basic: Event procedures Independent Sub procedures Event procedure: Associated with specific object and event Processed automatically in response to event Independent Sub procedure: Independent of any object and event Invoked from code using Call statement Parameter: Data passed to procedure when invoked 6 Programming with Microsoft Visual Basic 2008, Fourth Edition

7. Sub Procedures (continued) Call statement: Used to invoke procedure Syntax: Call procedurename([argumentlist]) argumentlist: Used to pass information (optional) Argument: Data item in argumentlist Parameter: Data item in parameterlist Relationship between arguments and parameters Should agree in number, position, and data type Types of data that can be passed as arguments to a procedure: Variable, literal constant, named constant, keyword 7 Programming with Microsoft Visual Basic 2008, Fourth Edition

8. Sub Procedures (continued) 8 Programming with Microsoft Visual Basic 2008, Fourth Edition

9. Passing Variables A variable has value and unique address in memory You can pass either variable’s value or its address to procedure Passing by value: Passes copy of value stored in variable Passing by reference: Passes memory address of variable Allows procedure to change contents of variable 9 Programming with Microsoft Visual Basic 2008, Fourth Edition

10. Passing a Variable by Value Passing 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 10 Programming with Microsoft Visual Basic 2008, Fourth Edition

11. Passing a Variable by Value (continued) 11 Programming with Microsoft Visual Basic 2008, Fourth Edition

12. 12 Programming with Microsoft Visual Basic 2008, Fourth Edition Passing a Variable by Value (continued)

13. Passing a Variable by Reference Passing 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 13 Programming with Microsoft Visual Basic 2008, Fourth Edition

14. 14 Programming with Microsoft Visual Basic 2008, Fourth Edition Passing a Variable by Reference (continued)

15. Passing a Variable by Reference (continued) 15 Programming with Microsoft Visual Basic 2008, Fourth Edition

16. Passing a Variable by Reference (continued) 16 Programming with Microsoft Visual Basic 2008, Fourth Edition

17. Passing a Variable by Reference (continued) 17 Programming with Microsoft Visual Basic 2008, Fourth Edition

18. Passing a Variable by Reference (continued) 18 Programming with Microsoft Visual Basic 2008, Fourth Edition

19. Passing a Variable by Reference (continued) 19 Programming with Microsoft Visual Basic 2008, Fourth Edition

20. 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 Return expression type must agree with As datatype 20 Programming with Microsoft Visual Basic 2008, Fourth Edition

21. 21 Programming with Microsoft Visual Basic 2008, Fourth Edition Function Procedures (continued)

22. Function Procedures (continued) 22 Programming with Microsoft Visual Basic 2008, Fourth Edition

23. Function Procedures (continued) 23 Programming with Microsoft Visual Basic 2008, Fourth Edition

24. Lesson A Summary Two types of procedures: Event and independent Function: Performs task and returns value Independent procedures and functions are 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 24 Programming with Microsoft Visual Basic 2008, Fourth Edition

25. 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 25 Programming with Microsoft Visual Basic 2008, Fourth Edition

26. 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 26 Programming with Microsoft Visual Basic 2008, Fourth Edition

27. Including a Combo Box in an Interface (continued) 27 Programming with Microsoft Visual Basic 2008, Fourth Edition

28. Including a Combo Box in an Interface (continued) Change in item value causes TextChanged event 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: Determines which item is selected Text: Used to get or set value in text portion 28 Programming with Microsoft Visual Basic 2008, Fourth Edition

29. 29 Programming with Microsoft Visual Basic 2008, Fourth Edition Including a Combo Box in an Interface (continued)

30. Including a Combo Box in an Interface (continued) 30 Programming with Microsoft Visual Basic 2008, Fourth Edition

31. Lesson B Summary Combo box displays list of items for selection Combo box allows user to type entry not on list 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 31 Programming with Microsoft Visual Basic 2008, Fourth Edition

32. Lesson B Summary (continued) Use SelectedIndex, SelectedItem, or Text property to select combo box item from code Use SelectedIndex, SelectedItem, or Text property to determine item that was selected 32 Programming with Microsoft Visual Basic 2008, Fourth Edition

33. Lesson C Objectives After studying Lesson C, you should be able to: Prevent a form from closing Round a number 33 Programming with Microsoft Visual Basic 2008, Fourth Edition

34. Coding the Harvey Industries Application Objective: Calculate employee’s weekly gross pay, federal withholding tax (FWT), Social Security and Medicare (FICA) tax, and net pay Review TOE chart for requirements 34 Programming with Microsoft Visual Basic 2008, Fourth Edition

35. 35 Programming with Microsoft Visual Basic 2008, Fourth Edition Coding the Harvey Industries Application (continued)

36. 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 Cancel property of FormClosing procedure’s e parameter to true 36 Programming with Microsoft Visual Basic 2008, Fourth Edition

37. Coding the FormClosing Event Procedure (continued) 37 Programming with Microsoft Visual Basic 2008, Fourth Edition

38. Coding the FormClosing Event Procedure (continued) 38 Programming with Microsoft Visual Basic 2008, Fourth Edition

39. 39 Programming with Microsoft Visual Basic 2008, Fourth Edition Coding the FormClosing Event Procedure (continued)

40. Coding the btnCalc Control’s Click Event Procedure 40 Programming with Microsoft Visual Basic 2008, Fourth Edition

41. Coding the GetFwt Function How to calculate weekly taxable wages: Multiply number of withholding allowances by $67.31 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 41 Programming with Microsoft Visual Basic 2008, Fourth Edition

42. Coding the GetFwt Function (continued) 42 Programming with Microsoft Visual Basic 2008, Fourth Edition

43. Coding the GetFwt Function (continued) 43 Programming with Microsoft Visual Basic 2008, Fourth Edition

44. Coding the GetFwt Function (continued) 44 Programming with Microsoft Visual Basic 2008, Fourth Edition

45. Coding the GetFwt Function (continued) 45 Programming with Microsoft Visual Basic 2008, Fourth Edition

46. Completing the btnCalc Control’s Click Event Procedure Must call GetFwt function from btnCalc’s Click event procedure Math.Round function: Used to round value to specific number of decimal places Syntax: Math.Round (value[, digits]) value: Numeric value to work on digits: Number of places to right of decimal point 46 Programming with Microsoft Visual Basic 2008, Fourth Edition

47. Completing the btnCalc Control’s Click Event Procedure (continued) 47 Programming with Microsoft Visual Basic 2008, Fourth Edition

48. 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 48 Programming with Microsoft Visual Basic 2008, Fourth Edition