1. Chapter Ten Structures and Sequential Access Files Programming with Microsoft Visual Basic 2010 5 th Edition

2. Programming with Microsoft Visual Basic 2010, 5 th Edition Previewing the CD Collection Application 2 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

3. Programming with Microsoft Visual Basic 2010, 5 th Edition Previewing the CD Collection Application (cont’d.) 3 Figure 10-1 CD information added to the list box

4. Programming with Microsoft Visual Basic 2010, 5 th Edition Previewing the CD Collection Application (cont’d.) 4 Figure 10-2 Contents of the CDs.txt file

5. Programming with Microsoft Visual Basic 2010, 5 th Edition Lesson A Objectives 5 After studying Lesson A, you should be able to: Create a structure Declare and use a structure variable Pass a structure variable to a procedure Create an array of structure variables

6. Programming with Microsoft Visual Basic 2010, 5 th Edition Structures 6 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

7. Programming with Microsoft Visual Basic 2010, 5 th Edition Structures (cont’d.) 7 Figure 10-3 Syntax and an example of the Structure statement

8. Programming with Microsoft Visual Basic 2010, 5 th Edition Declaring and Using a Structure Variable 8 Structure variables: Declared using structure Structure is data type for variable Example: Dim hourly As Employee hourly is variable declared with Employee structure type Accessing member variable in code Use structureVariableName. memberVariableName Example: hourly.dblPay = 26 Member variables are used like scalar variables

9. Programming with Microsoft Visual Basic 2010, 5 th Edition Declaring and Using a Structure Variable (cont’d.) 9 Figure 10-4 Syntax and examples of declaring a structure variable

10. Programming with Microsoft Visual Basic 2010, 5 th Edition 10 Figure 10-5 Examples of using a member variable

11. Programming with Microsoft Visual Basic 2010, 5 th Edition Passing a Structure Variable to a Procedure 11 Application for sales manager at Willow Pools Allows user to enter length, width, and depth Calculates gallons of water to fill 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

12. Programming with Microsoft Visual Basic 2010, 5 th Edition 12 Figure 10-7 Code for the Willow Pools application (without a structure)

13. Programming with Microsoft Visual Basic 2010, 5 th Edition 13 Figure 10-8 Code for the Willow Pools application (with a structure)

14. Programming with Microsoft Visual Basic 2010, 5 th Edition Lesson A Summary 14 Structures: User-defined data types Structure members can be variables, constants, or procedures Refer to member within structure variable using structureVariableName.memberVariableName To create an array of structure variables: Declare array using structure as data type Refer to member within structure variable stored in an array using: arrayName(subscript).memberVariableName

15. Programming with Microsoft Visual Basic 2010, 5 th Edition Lesson B Objectives 15 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

16. Programming with Microsoft Visual Basic 2010, 5 th Edition Sequential Access Files 16 Reading a file: Getting data from a file Writing to a file: Sending data to a file Output files: Store application output Input files: Application uses data in these files Sequential access files Composed of lines of text that are both read and written in consecutive order Also called text files

17. Programming with Microsoft Visual Basic 2010, 5 th Edition Writing Data to a Sequential Access File 17 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 application Uses StreamWriter variable

18. Programming with Microsoft Visual Basic 2010, 5 th Edition Writing Data to a Sequential Access File (cont’d.) 18 Figure 10-15 Syntax and an example of declaring a StreamWriter variable

19. Programming with Microsoft Visual Basic 2010, 5 th Edition 19 Figure 10-17 Syntax and examples of the CreateText and AppendText methods

20. Programming with Microsoft Visual Basic 2010, 5 th Edition 20 Figure 10-18 Syntax and examples of the Write and WriteLine methods

21. Programming with Microsoft Visual Basic 2010, 5 th Edition Closing an Output Sequential Access File 21 Close method Used to close an output sequential access file Figure 10-19 Syntax and an example of closing an output sequential access file

22. Programming with Microsoft Visual Basic 2010, 5 th Edition Reading Data from a Sequential Access File 22 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

23. Programming with Microsoft Visual Basic 2010, 5 th Edition 23 Figure 10-21 Syntax and an example of declaring a StreamReader variable

24. Programming with Microsoft Visual Basic 2010, 5 th Edition 24 Figure 10-22 Syntax and an example of the OpenText method

25. Programming with Microsoft Visual Basic 2010, 5 th Edition 25 Figure 10-23 Syntax and an example of the Exists method

26. Programming with Microsoft Visual Basic 2010, 5 th Edition 26 Figure 10-24 Additional code entered in the procedure

27. Programming with Microsoft Visual Basic 2010, 5 th Edition Reading Data from a Sequential Access File (cont’d.) 27 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

28. Programming with Microsoft Visual Basic 2010, 5 th Edition 28 Figure 10-25 Syntax and an example of the ReadLine method

29. Programming with Microsoft Visual Basic 2010, 5 th Edition 29 Figure 10-26 Syntax and an example of the Peek method

30. Programming with Microsoft Visual Basic 2010, 5 th Edition Closing an Input Sequential Access File 30 Close method Used to close input sequential access files Figure 10-27 Syntax and an example of closing an input sequential access file