1. Using Arrays and File Handling
CHAPTER EIGHT
Using Arrays and File Handling

2. Objectives Initialize an array Initialize an array with default values
Access array elements using a loop
Use ReDim to resize an array
Determine the number of elements in an array using the Length command
Use the For Each loop
Chapter 8: Using Arrays and File Handling

3. Objectives Initialize two-dimensional arrays Read a text file
Write to a text file
Calculate depreciation
Use multiple Form objects
Access Variable objects on other forms
Chapter 8: Using Arrays and File Handling

4. Introduction
Chapter 8: Using Arrays and File Handling

5. Introduction to Arrays
An array variable is simply a variable that can store more than one value
Each individual item in array that contains a value is called an element
Arrays provide access to data by using a numeric index, or subscript, to identify each element in the array
Chapter 8: Using Arrays and File Handling

6. Initializing an Array
To declare an array in a program, you must include an array declaration statement, which states the name of the array, how many items it can store, and what sort of data it can store
Chapter 8: Using Arrays and File Handling

7. Initializing an Array
Parallel arrays store related data in two or more arrays
Chapter 8: Using Arrays and File Handling

8. Accessing Array Elements Using a Loop
Chapter 8: Using Arrays and File Handling

9. Introduction to Arrays
The Visual Basic compiler determines if each subscript is within the boundaries set when you initialized the array
An array can use a constant value representing the upper-bound index
Every array in Visual Basic is considered dynamic, which means that you can resize it at run time
The ReDim statement assigns a new array size to the specified array variable
All data in the array will be lost
If you want to preserve the existing data you can use the keyword Preserve
Ex: ReDim Preserve
Chapter 8: Using Arrays and File Handling

10. Using the Length Property
The Length property of an array contains the number of elements in an array
Chapter 8: Using Arrays and File Handling

11. Using Arrays
Chapter 8: Using Arrays and File Handling

12. The For Each Loop
Chapter 8: Using Arrays and File Handling

13. The For Each Loop
Chapter 8: Using Arrays and File Handling

14. Scope of Arrays
The scope of an array declared within a procedure is local to that procedure, but an array can be declared as a class level variable
Chapter 8: Using Arrays and File Handling

15. Passing an Array
An array can be passed as an argument to a Sub procedure or a Function procedure
Chapter 8: Using Arrays and File Handling

16. Sorting an Array
Chapter 8: Using Arrays and File Handling

17. Searching an Array
Searching each element in an array is called a sequential search
The BinarySearch method searches a sorted array for a value using a binary search algorithm
The binary search algorithm searches an array by repeatedly dividing the search interval in half
Chapter 8: Using Arrays and File Handling

18. Creating a Two-Dimensional Array
A two-dimensional array holds data that is arranged in rows and columns
Chapter 8: Using Arrays and File Handling

19. Creating a Two-Dimensional Array
Chapter 8: Using Arrays and File Handling

20. File Handling
To process data more efficiently, many developers use text files to store and access information to use within an application
Text files have a .txt extension
A simple text file is called a sequential file
Chapter 8: Using Arrays and File Handling

21. Reading a Text File
To open a text file, you need an object available in the System.IO called a StreamReader
Chapter 8: Using Arrays and File Handling

22. Reading a Text File
To determine whether the end of the file has been reached, use the Peek procedure of the StreamReader object
Chapter 8: Using Arrays and File Handling

23. Reading a Text File
Open the code window by tapping or clicking the View Code button on the Solution Explorer toolbar. Tap or click inside the frmDepreciation_Load event
Initialize the variables. Assign an object variable to the IO.StreamReader object. Initialize the StreamReader object by typing Dim objReader As IO. An IntelliSense window opens. Select StreamReader. Press ENTER. Finish declaring the rest of the variable names
Verify that the inventory.txt data file is available by typing If IO. to open an IntelliSense window. Complete the rest of the line using IntelliSense as shown on the following slide. Assign the objReader variable by typing objR and then pressing CTRL + SPACEBAR to complete the variable name. Type = IO. and IntelliSense opens. Type F
Chapter 8: Using Arrays and File Handling

24. Reading a Text File
Chapter 8: Using Arrays and File Handling

25. Reading a Text File
Select File by typing a period and select OpenText from the IntelliSense list. Type (“e:\inventory.txt”) to access the inventory text file from the USB drive (drive E)
To read each line of the text file, insert a Do While loop that continues until the Peek procedure returns the value of -1. Specify that the ReadLine() procedure reads each line of the text file. Use the variable intCount to determine the index of each array element
After the data file has been read, close the file. Insert an Else statement that informs the user if the file cannot be opened and closes the application
Chapter 8: Using Arrays and File Handling

26. Reading a Text File
Chapter 8: Using Arrays and File Handling

27. Writing to a Text File
Writing to a text file is similar to reading a text file. The System.IO namespace also includes the StreamWriter, which is used to write a stream of text to a file
Chapter 8: Using Arrays and File Handling

28. Writing to a Text File
Chapter 8: Using Arrays and File Handling

29. Computing Depreciation
Depreciation is the decrease in property value and the reduction in the balance sheet value of a company asset to reflect its age and prolonged use
The simplest and most common method, straight-line depreciation, is calculated by dividing the purchase or acquisition price of an asset by the total productive years the asset can reasonably be expected to benefit the company, which is called the life of the asset
Chapter 8: Using Arrays and File Handling

30. Computing Depreciation
The double-declining balance depreciation method is like the straight-line method doubled
Chapter 8: Using Arrays and File Handling

31. Using Multiple Form Objects
Tap or click PROJECT on the menu bar, and then tap or click Add Windows Form
In the Add New Item dialog box, tap or click Windows Form, and then type frmDisplayInventory.vb in the Name text box
Click the Add button in the Add New Item dialog box. A second Form object named frmDisplayInventory.vb opens in the Visual Basic 2012 window. In the Properties window, change the Text property of the frmDisplayInventory object to Sorted Inventory Listing
Chapter 8: Using Arrays and File Handling

32. Using Multiple Form Objects
Chapter 8: Using Arrays and File Handling

33. Startup Objects
Every application begins executing a project by displaying the object designated as the Startup object
Chapter 8: Using Arrays and File Handling

34. Creating an Instance of a Windows Form Object
To display a second or subsequent form, the initial step in displaying the form is to create an instance of the Windows Form object
When creating multiple Windows Form objects, Visual Basic allows you to generate two types of forms: modal and modeless
A modal form retains the input focus while open
A modeless form allows you to switch the input focus to another window
Chapter 8: Using Arrays and File Handling

35. Creating an Instance of a Windows Form Object
Chapter 8: Using Arrays and File Handling

36. Accessing Variables on Other Forms
You control the availability of a variable by specifying its access level, or access specifier
Chapter 8: Using Arrays and File Handling

37. Program Design
Chapter 8: Using Arrays and File Handling

38. Program Design
Chapter 8: Using Arrays and File Handling

39. Designing the Program Processing Objects
Chapter 8: Using Arrays and File Handling

40. Designing the Program Processing Objects
Chapter 8: Using Arrays and File Handling

41. Designing the Program Processing Objects
Chapter 8: Using Arrays and File Handling

42. Designing the Program Processing Objects
Chapter 8: Using Arrays and File Handling

43. Summary Initialize an array Initialize an array with default values
Access array elements using a loop
Use ReDim to resize an array
Determine the number of elements in an array using the Length command
Use the For Each loop
Chapter 8: Using Arrays and File Handling 43

44. Summary Initialize two-dimensional arrays Read a text file
Write to a text file
Calculate depreciation
Use multiple Form objects
Access Variable objects on other forms
Chapter 8: Using Arrays and File Handling 44

45. CHAPTER EIGHT COMPLETE
Using Arrays and File Handling