1. CIS16 Application Development and Programming using Visual Basic.net
Chapter Nine
Structures and Sequential Files

2. STRUCTURES

3. Structures Structures are objects you can create to hold data or code
Used when you need to pass a group of related items to a procedure for further processing, or to store related items in an Array
Structure statement is defined in the Declarations section of the class –NOT inside a SUB

4. Structures Like an Array Like a record in a table
in that related items are grouped into list
Like a record in a table
in that related items are grouped together with a unique identifier

5. Structures Inside the structure are the items (members)
Items can have different data types, and can be variables, constants or procedures
Use Pascal case when defining items

6. Structures (cont'd.) Variables Referred to as Member Variables
Each member variable’s definition contains the keyword Public followed by the variable’s name and data type

7. Structures (cont'd.)
Structures can be instantiated into structure variable objects
structure variable is an object declared using a structure as its data type rather than a true data type
If declaring a structure variable object in a procedure
Use the Dim keyword
If declaring a structure variable object in a Class
use the Private keyword

8. Structures (cont'd.)
Instantiating

9. Structures (cont'd.)
Populating

10. Creating an Array of Structure Variables

11. Creating an Array of Structure Variables
a structure variable can be stored in an array, even when its members have different data types

12. Sequential Access Files

13. Reading and Writing Records
Sequential files can be used to store records and fields
A field is a single item of information about a person, place, or thing
A record is a group of related fields that contain all of the necessary data about a specific person, place, or thing
When writing records to a sequential access file, programmers typically write each record on a separate line in the file
They use a special character, called a delimiter character, to separate each field
Commonly used delimiter characters include the comma and the number (or hash) sign (#)

14. Sequential Access Files
Input files
An application uses the data in these files as input
Output files
Files that store the output produced by an application
Sequential access files
Composed of lines of text that are both read and written sequentially (in consecutive order), one line at a time
Also called text files

15. Sequential Access File Objects
StreamWriter object
Allows you to write a stream of characters to a sequential access file
StreamReader object
Used to read data streams from a sequential access file

16. STREAMWRITER Methods: CreateText() AppendText() Write() WriteLine()
Close()
STREAMWRITER

17. StreamWriter Used to write data to a sequential access file
StreamWriter object
Allows you to write a stream of characters to a sequential access file
Define Writer as procedure/class level object

18. StreamWriter Used to write data to a sequential access file
CreateText method
Used to open a sequential access file for output (creates a new, empty file)
Unless otherwise specified, gets created in the bin/Debug folder

19. StreamWriter Used to write data to a sequential access file
Write method
When using the Write method, the next character written to the file will appear immediately after the last letter in the string
WriteLine method
When using the WriteLine method, the next character written to the file will appear on the line immediately below the string

20. StreamWriter Used to write data to a sequential access file
AppendText method
Used to open a sequential access file for append(new data is written after existing data)

21. StreamWriter Used to write data to a sequential access file
Use the Close method to close an output sequential access file
Ensures that the data is saved and it makes the file available for use elsewhere in the application

22. Writing Records (cont'd.)
When writing records, separate fields using a delimiter

23. Methods:
OpenText()
Peek()
ReadLine()
Close()
STREAMREADER

24. StreamReader Used to read data from a sequential access file
Define StreamReader as a procedure/class level object(s)

25. StreamReader Used to read data from a sequential access file
Before using it, use EXISTS method to make sure it actually was created
Exists method
Returns the Boolean value True if the file exists; otherwise, it returns the Boolean value False

26. StreamReader Used to read data from a sequential access file
The OpenText method opens a sequential access file for input, and creates an instance of the Reader
Unless otherwise specified, looks for it in the bin/Debug folder

27. StreamReader Used to read data from a sequential access file
Peek method
“Peeks” into the file to determine whether it contains another line to read
-1 indicates EOF

28. StreamReader Used to read data from a sequential access file
The ReadLine method reads the file’s contents, one line (characters followed by the newline character) at a time

29. StreamReader Used to read data from a sequential access file
The Close method closes the file

30. Reading Records
To Read records with multiple fields, use Split function
Separates fields in record, creating a String array
Specify delimiter, and data type conversion, if necessary

31. Adding a Menu to a Form Menu strip control
Used to include one or more menus on a form
A menu title appears on the menu bar at the top of the form
Menu items can include:
Commands
Submenu items
Separator bars
Clicking a command on a menu executes it
Clicking a submenu item opens an additional menu
Separator bars provide visual grouping

32. Adding a Menu to a Form (cont.)
Menu title captions should be one word only
Menu item captions can be from one to three words
Assign unique access keys to menu titles and items
Follow Windows menu standards:
Use book title capitalization for menu item captions
An ellipsis (…) after an item caption indicates a menu item requires more information
The FILE menu should be the first item on the menu bar
Cut, Copy, and Paste should appear on the EDIT menu

33. Adding a Menu to a Form Menu Strip Control
To include one or more menus on a Form
The shortcut keys appear to the right of a menu item and allow the user to select the item without opening the menu

34. Adding a Menu to a Form (cont'd.)
Figure 10-9: FILE menu

35. Adding a Menu to a Form (cont.)
Assigning Shortcut Keys to Menu Items
Shortcut keys
Appear to the right of a menu item
Allow the user to select an item without opening a menu
Example: Ctrl+X and Ctrl+V
Cut and paste commands
Assign shortcut keys to commonly used menu items
Follow Windows standard conventions
Shortcut keys can be used when a menu is closed

36. Adding a Menu to a Form (cont.)
Assigning Shortcut Keys to Menu Items (cont.)
Figure 8-28 Location of the shortcut keys on the menu
Figure 8-27 Shortcut keys specified in the ShortcutKeys box

37. Adding a Menu to a Form (cont.)
Coding the Exit Menu Item
How to end the Pizza Game application:
The user clicks the Exit item on the FILE menu
The Exit item’s Click event procedure calls Me.Close()
Coding the txtLetter Control’s KeyPress Event
Figure 8-29 txtLetter_KeyPress procedure