Programming with Microsoft Visual Basic 2008 Fourth Edition

1. Programming with Microsoft Visual Basic 2008 Fourth Edition Chapter Ten Structures and Sequential Access Files

2. Previewing the CD Collection Application CD Collection Application: Keeps track of person’s CD collection Saves each CD’s name, artist’s name, and price Uses sequential access file named CDs.txt Can add to or remove information from file Open the CD.exe file Programming with Microsoft Visual Basic 2008, Fourth Edition 2

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

4. Previewing the CD Collection Application (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 4

5. Lesson A Objectives After studying Lesson A, you should be able to: Create a structure Declare a structure variable Pass a structure variable to a procedure Create and manipulate a one-dimensional array of structures Programming with Microsoft Visual Basic 2008, Fourth Edition 5

6. Creating a Structure Structure statement: Enables you to create your own data types Used to group related items of different data types into one unit Typically appears in form’s Declaration section Structure (or user-defined data type): Data type created with Structure statement Member variables: Variables, constants, or procedures declared within structure declaration Programming with Microsoft Visual Basic 2008, Fourth Edition 6

7. Creating a Structure (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 7

8. Declaring and Using a Structure Variable Structure variables: Declared using structure Structure is data type for variable Example: Dim manager As Employee manager is variable declared with Employee structure type Accessing member variable in code: Use structureVariableName. memberName Example: manager.dblSalary = 59000D Member variables are used like scalar variables Programming with Microsoft Visual Basic 2008, Fourth Edition 8

9. Declaring and Using a Structure Variable (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 9

10. Declaring and Using a Structure Variable (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 10

11. Passing a Structure Variable to a Procedure Application for sales manager at Willows Pool: Allows user to enter length, width, and depth Calculates volume of pool Advantages of using structure to group dimensions: Three inputs are stored in one structure variable You pass single structure variable to procedure instead of three scalar variables Your code is structured in more readable form Programming with Microsoft Visual Basic 2008, Fourth Edition 11

12. Programming with Microsoft Visual Basic 2008, Fourth Edition 12 Passing a Structure Variable to a Procedure (continued)

13. Programming with Microsoft Visual Basic 2008, Fourth Edition 13 Passing a Structure Variable to a Procedure (continued)

14. Creating an Array of Structure Variables Three ways to manage pairs of ID-price data: Two parallel one-dimensional arrays One two-dimensional array (tabular format) One-dimensional array of structure variables Structure variable will contain: String variable for ID Integer variable for price Programming with Microsoft Visual Basic 2008, Fourth Edition 14

15. Programming with Microsoft Visual Basic 2008, Fourth Edition 15 Creating an Array of Structure Variables (continued)

16. Creating an Array of Structure Variables (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 16

17. Lesson A Summary Structures are user-defined data types Structure members can be variables, constants, or procedures Refer to member within structure variable using structureVariableName.memberName Element in array of structure variables is structure variable Refer to member within structure variable stored in an array using: arrayName(subscript).memberName Programming with Microsoft Visual Basic 2008, Fourth Edition 17

18. Lesson B Objectives After studying Lesson B, you should be able to: Open and close a sequential access file Write data to a sequential access file Read data from a sequential access file Determine whether a sequential access file exists Test for the end of a sequential access file Programming with Microsoft Visual Basic 2008, Fourth Edition 18

19. Sequential Access Files Reading a file: Getting data from a file Writing to a file: Sending data to a file Output files: Files to which information is written Input files: Files that are read by a computer Sequential access files: Files composed of lines of text that are both read and written sequentially Programming with Microsoft Visual Basic 2008, Fourth Edition 19

20. Writing Data to a Sequential Access File Stream of characters: Sequence of characters StreamWriter object: Used to write stream of characters to sequential access file Must declare StreamWriter variable Game Show Contestants sample application uses StreamWriter variable Programming with Microsoft Visual Basic 2008, Fourth Edition 20

21. Writing Data to a Sequential Access File (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 21

22. Writing Data to a Sequential Access File (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 22

23. Writing Data to a Sequential Access File (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 23

24. Writing Data to a Sequential Access File (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 24

25. Reading Data From a Sequential Access File StreamReader object: Used to read data from sequential access file Must declare StreamReader variable OpenText method: Used to open sequential access file for input Can use this method to automatically create StreamReader object Exists method: Used to determine if file exists Returns True if file exists, otherwise False Programming with Microsoft Visual Basic 2008, Fourth Edition 25

26. Reading Data From a Sequential Access File (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 26

27. Reading Data From a Sequential Access File (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 27

28. Reading Data From a Sequential Access File (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 28

29. Reading Data From a Sequential Access File (continued) Line: Sequence (stream) of characters followed by newline character ReadLine method: Used to read contents of file, one line at a time Returns String value containing data in current line Returns only data, not including newline character Peek method: Determines whether file contains another character to read Programming with Microsoft Visual Basic 2008, Fourth Edition 29

30. Reading Data From a Sequential Access File (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 30

31. Programming with Microsoft Visual Basic 2008, Fourth Edition 31 Reading Data From a Sequential Access File (continued)

32. Programming with Microsoft Visual Basic 2008, Fourth Edition 32 Reading Data From a Sequential Access File (continued)

33. Programming with Microsoft Visual Basic 2008, Fourth Edition 33

34. Lesson B Summary Sequential access file: Stores data items in consecutive order (sequentially) Use StreamWriter variable to write data to sequential access file Use StreamReader variable to read data from sequential access file Use Exists method to determine if file exists Use Peek method to determine whether end of sequential access file has been reached Programming with Microsoft Visual Basic 2008, Fourth Edition 34

35. Lesson C Objectives After studying Lesson C, you should be able to: Fill a list box with values stored in a sequential access file Add an item to a list box while an application is running Align columns of information Remove an item from a list box while an application is running Save list box items in a sequential access file Programming with Microsoft Visual Basic 2008, Fourth Edition 35

36. Coding the CD Collection Application Programming with Microsoft Visual Basic 2008, Fourth Edition 36

37. Coding the CD Collection Application (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 37

38. Coding the CD Collection Application (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 38

39. Coding the Form’s Load Event Procedure Programming with Microsoft Visual Basic 2008, Fourth Edition 39

40. Coding the Form’s Load Event Procedure (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 40

41. Coding the Form’s Load Event Procedure (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 41

42. Coding the btnAdd Control’s Click Event Procedure Programming with Microsoft Visual Basic 2008, Fourth Edition 42

43. 43 Programming with Microsoft Visual Basic 2005, Third Edition Aligning Columns of Information PadLeft and PadRight methods: Used to pad strings with characters These methods can be used to align text in list box or text written to sequential access file Strings.Space method: Used to include specific number of space characters in string Syntax: Strings.Space(number) number: Integer representing number of spaces to include

44. Coding the btnRemove Control’s Click Event Procedure Main task: Allow user to remove selected line from list box control RemoveAt method: Removes list box item at specified index Programming with Microsoft Visual Basic 2008, Fourth Edition 44

45. Coding the btnRemove Control’s Click Event Procedure (continued) Programming with Microsoft Visual Basic 2008, Fourth Edition 45

46. Coding the Form’s FormClosing Event Procedure Programming with Microsoft Visual Basic 2008, Fourth Edition 46

47. Lesson C Summary Use Add method of list box to add an item to list Use PadLeft method to right-align string, or to align column of numbers by decimal point Use PadRight method to left-align string Use Strings.Space method to include specific number of spaces in string Use RemoveAt method to remove item at specific index from listbox Programming with Microsoft Visual Basic 2008, Fourth Edition 47