1. Microsoft Visual Basic 2005: Reloaded Second Edition Chapter 9 Structures and Sequential Access Files

2. Microsoft Visual Basic 2005: Reloaded, Second Edition2 Structures Structure statement: creates your own data type User-defined data type (or structure): data types created by using the Structure statement Member variables: variables defined within a structure Structure can include member variables of: –Any of the standard data types –Other structure types

3. Microsoft Visual Basic 2005: Reloaded, Second Edition3 Structures (continued)

4. Microsoft Visual Basic 2005: Reloaded, Second Edition4 Using a Structure to Declare a Variable Structure variables: variables declared using a structure Refer to an entire structure in code using its name Refer to a member variable using the structure name with the dot operator and the member variable name Member variables can be used like any other variables Structures are used to group related items into one unit

5. Microsoft Visual Basic 2005: Reloaded, Second Edition5 Using a Structure to Declare a Variable (continued)

6. Microsoft Visual Basic 2005: Reloaded, Second Edition6 Using a Structure to Declare a Variable (continued)

7. Microsoft Visual Basic 2005: Reloaded, Second Edition7 Passing a Structure Variable to a Procedure Open the Pool program and Flow Chart

8. Microsoft Visual Basic 2005: Reloaded, Second Edition8 Passing a Structure Variable to a Procedure (continued) Sample application using a structure: –Less code to pass a structure variable to a procedure –Stores all of the data in a single unit

9. Microsoft Visual Basic 2005: Reloaded, Second Edition9 Creating an Array of Structure Variables Use a one-dimensional array of structure variables instead of two-dimensional or parallel one- dimensional arrays Refer to a member variable in an array element by: arrayname(subscript).memberVariableName

10. Microsoft Visual Basic 2005: Reloaded, Second Edition10 Creating an Array of Structure Variables (continued)

11. Microsoft Visual Basic 2005: Reloaded, Second Edition11 Creating an Array of Structure Variables (continued)

12. Microsoft Visual Basic 2005: Reloaded, Second Edition12 Creating an Array of Structure Variables (continued)

13. Microsoft Visual Basic 2005: Reloaded, Second Edition13 Creating an Array of Structure Variables (continued)

14. Microsoft Visual Basic 2005: Reloaded, Second Edition14 File Types Reading a file: getting information from a file Writing to a file: sending information to a file Output files: files to which information is written Input files: files that are read by the computer Three types of files in Visual Basic: –Sequential –Random –Binary

15. Microsoft Visual Basic 2005: Reloaded, Second Edition15 File Types (continued) Sequential file: data is accessed sequentially, in consecutive order from the beginning to the end Random file: data can be accessed in consecutive or random order Binary file: data is accessed by its byte location in the file

16. Microsoft Visual Basic 2005: Reloaded, Second Edition16 Sequential Access Files Sequential access file: often called a text file because it is composed of lines of text Data must be read sequentially from beginning to end

17. Microsoft Visual Basic 2005: Reloaded, Second Edition17 Sequential Access Files (continued)

18. Microsoft Visual Basic 2005: Reloaded, Second Edition18 Writing Information to a Sequential Access File WriteAllText method: –Writes information to a sequential access file –File argument: contains the name of the file to be used –Text argument: contains the data to be written –Append argument: if True, data is added to end of existing file; otherwise all existing data is erased

19. Microsoft Visual Basic 2005: Reloaded, Second Edition19 Writing Information to a Sequential Access File (continued) My feature: exposes a set of commonly used objects to the programmer My.Computer object: allows access to objects and methods to manipulate files Computer uses a file pointer to trace where the next character will be read from or written to a file Strings.Space method: writes a specific number of spaces to a file

20. Microsoft Visual Basic 2005: Reloaded, Second Edition20 Writing Information to a Sequential Access File (continued)

21. Microsoft Visual Basic 2005: Reloaded, Second Edition21 Aligning Columns of Information in a Sequential Access File PadLeft, PadRight methods: –Pads a string with a specified number of characters based on current length of the string being padded –Aligns columns of information written to a sequential access file Aligns columns of numeric information by the decimal point

22. Microsoft Visual Basic 2005: Reloaded, Second Edition22 Aligning Columns of Information in a Sequential Access File (continued)

23. Microsoft Visual Basic 2005: Reloaded, Second Edition23 Aligning Columns of Information in a Sequential Access File (continued)

24. Microsoft Visual Basic 2005: Reloaded, Second Edition24 Reading Information from a Sequential Access File ReadAllText method: reads information stored in a sequential access file –File argument: contains the name of the sequential access file

25. Microsoft Visual Basic 2005: Reloaded, Second Edition25 Reading Information from a Sequential Access File (continued)

26. Microsoft Visual Basic 2005: Reloaded, Second Edition26 Determining Whether a File Exists An attempt to read a file that does not exist will cause an error FileExists method: determines if the file exists before attempting to read it –File argument: contains the name of the file

27. Microsoft Visual Basic 2005: Reloaded, Second Edition27 Determining Whether a File Exists (continued)

28. Microsoft Visual Basic 2005: Reloaded, Second Edition28 The FormClosing Event FormClosing event: –Occurs when a form is about to be closed by the program code or by the user –Allows you to trap the closing action and take any necessary actions such as saving data –Can be used to cancel the close action –Set e.Cancel = True to cancel the closing action

29. Microsoft Visual Basic 2005: Reloaded, Second Edition29 The FormClosing Event (continued)

30. Microsoft Visual Basic 2005: Reloaded, Second Edition30 The Friends Application