1. Variables and Arithmetic Operations
CHAPTER FOUR
Variables and Arithmetic Operations

2. Objectives Create, modify, and program a TextBox object
Use code to place data in the Text property of a Label object
Use the AcceptButton and CancelButton properties
Understand and declare String and Numeric variables
Use assignments statements to place data in variables
Chapter 4: Variables and Arithmetic Operations

3. Objectives Use literals and constants in coding statements
Understand scope rules for variables
Convert string and numeric data
Understand and use arithmetic operators and arithmetic operations
Chapter 4: Variables and Arithmetic Operations

4. Objectives Format and display numeric data as a string
Create a form load event
Create a concatenated string
Debug a program
Chapter 4: Variables and Arithmetic Operations

5. Introduction
Chapter 4: Variables and Arithmetic Operations

6. Preview the Chapter Project
Chapter 4: Variables and Arithmetic Operations

7. TextBox Objects
With Visual Studio open and the frmDigitalDownloads.vb [Design] tabbed page visible, point to the TextBox .NET component in the Toolbox
Drag the TextBox .NET component onto the Windows Form object at the desired location
When the upper-left corner of the pointer is located where you want the TextBox object’s upper-left corner, release the left mouse button
Chapter 4: Variables and Arithmetic Operations

8. TextBox Objects
Chapter 4: Variables and Arithmetic Operations

9. TextBox Objects
Chapter 4: Variables and Arithmetic Operations

10. Sizing and Positioning a TextBox Object
Select the TextBox object. Scroll in the Properties window until the Text property is visible and then click the right column for the Text property
Type the maximum number of characters the user normally will enter into the text box and then press the ENTER key. When entering numbers, the digit 8 often is entered because it is wider than other digits. In this example, the value 888 is entered because three digits is the maximum number of digits the user normally will enter
Chapter 4: Variables and Arithmetic Operations

11. Sizing and Positioning a TextBox Object
Using the Font property in the Properties window, change the Font property to the correct font and font size. For this application, change the font to Century Gothic and change the font size to 12. Then, drag the right edge of the TextBox object to resize the TextBox object so it is slightly wider than the 888 entry
To horizontally align the text in the label and the text in the text box, drag the text box up until a red snap line indicates the bottoms of the text are aligned. Then, release the left mouse button
Chapter 4: Variables and Arithmetic Operations

12. Sizing and Positioning a TextBox Object
Chapter 4: Variables and Arithmetic Operations

13. Sizing and Positioning a TextBox Object
Chapter 4: Variables and Arithmetic Operations

14. Aligning Text in a TextBox Object
Select the TextBox object. In the Properties window, scroll until the TextAlign property is visible, click the TextAlign property in the left column, and then click the list arrow in the right column of the TextAlign property
Click Center in the TextAlign property list
Because the TextBox object is sized properly, remove the digits in the TextBox object. Select the characters 888 in the Text property, press the DELETE key on your keyboard, and then press the ENTER key
Chapter 4: Variables and Arithmetic Operations

15. Aligning Text in a TextBox Object
Chapter 4: Variables and Arithmetic Operations

16. Aligning Text in a TextBox Object
Chapter 4: Variables and Arithmetic Operations

17. Creating a MultiLine Text Box
Select the TextBox object, click the Action tag, and point to the MultiLine check box
Click the MultiLine check box
Chapter 4: Variables and Arithmetic Operations

18. Creating a MultiLine Text Box
Chapter 4: Variables and Arithmetic Operations

19. Creating a MaskedTextBox Object
Chapter 4: Variables and Arithmetic Operations

20. Creating a MaskedTextBox Object
Chapter 4: Variables and Arithmetic Operations

21. Creating a MaskedTextBox Object
Drag a MaskedTextBox .NET component from the Toolbox to the Windows Form object. Then, click the Action tag on the TextBox object and point to the Set Mask command
Click Set Mask on the MaskedTextBox Tasks list and then click the Short date mask description in the Input Mask dialog box
Click the OK button in the Input Mask dialog box and then click anywhere in the Windows Form object
Chapter 4: Variables and Arithmetic Operations

22. Creating a MaskedTextBox Object
Chapter 4: Variables and Arithmetic Operations

23. Creating a MaskedTextBox Object
Chapter 4: Variables and Arithmetic Operations

24. Label Objects
Drag a Label object onto the Windows Form object to the correct location. Name the label lblTotalCostOfDownloads. Change the label to the appropriate font size (Century Gothic, 12 point). In the Text property for the Label object, enter the maximum number of characters ($888.88) that will appear in the label during execution of the program
Drag the Label object up until the red snap line appears. Then release the left mouse button
Chapter 4: Variables and Arithmetic Operations

25. Label Objects
Chapter 4: Variables and Arithmetic Operations

26. Label Objects
Chapter 4: Variables and Arithmetic Operations

27. Accept Button in Form Properties
The program will carry out the event handler processing associated with the Accept Button if the user clicks the button or if the user presses the ENTER key
Click a blank area in the Windows Form object to select it. Scroll in the Properties window until the AcceptButton property is visible. Click the AcceptButton property name in the left column and then click the AcceptButton property list arrow in the right column
Click btnCalculateCost in the AcceptButton property list
Chapter 4: Variables and Arithmetic Operations

28. Accept Button in Form Properties
Chapter 4: Variables and Arithmetic Operations

29. Cancel Button in Form Properties
When the user presses the ESC key, the event handler processing for the button identified as the Cancel button will be executed
Click a blank area in the Windows Form object to select it
Click the CancelButton property name in the left column in the Properties window for the Windows Form object, and then click the CancelButton list arrow
Click the button name (btnClear) in the CancelButton property list
Chapter 4: Variables and Arithmetic Operations

30. Visual Studio Preparation for Code Entry
With the Toolbox visible, click the Toolbox Close button. The Toolbox closes and the work area expands in size. To reshow the Toolbox after it has been closed, click the Toolbox button on the Standard toolbar
Chapter 4: Variables and Arithmetic Operations

31. Visual Studio Preparation for Code Entry
Chapter 4: Variables and Arithmetic Operations

32. String Data Type
A String data type allows every character available on the computer to be stored in it
The data type for the value the user enters in a TextBox object and that is stored in the Text property of the TextBox object is string
A variable is a named location in RAM where data is stored
A String variable is a named location in RAM that can store a string value
Chapter 4: Variables and Arithmetic Operations

33. String Data Type
Chapter 4: Variables and Arithmetic Operations

34. Assignment Statements
One method to place data in the variable is to use an assignment statement
Chapter 4: Variables and Arithmetic Operations

35. Assignment Statements
With Visual Studio displaying the code editing window and the insertion point located in the desired column, type Dim followed by a space. Then, type the name of the String variable you want to define, strNumberOfSongs on your keyboard
Press the SPACEBAR, type the word As and then press the SPACEBAR again
Because the entry should be String, type str on your keyboard
Press the ENTER key
Chapter 4: Variables and Arithmetic Operations

36. Assignment Statements
To begin the assignment statement, type strn. IntelliSense displays the only variable name that starts with the letter strn, the String variable strNumberOfDownloads
Press the SPACEBAR, press the EQUAL SIGN key, and then press the SPACEBAR
Type me. to display the IntelliSense list, and then type txt to identify the txtNumberOfSongs TextBox object in the IntelliSense list
Press the PERIOD key and then, if necessary, type te to highlight the Text entry in the IntelliSense list
Press the ENTER key
Chapter 4: Variables and Arithmetic Operations

37. Assignment Statements
Chapter 4: Variables and Arithmetic Operations

38. Assignment Statements
Chapter 4: Variables and Arithmetic Operations

39. Numeric Data Types
A numeric data type must be used in arithmetic operations
Chapter 4: Variables and Arithmetic Operations

40. Numeric Data Types
Chapter 4: Variables and Arithmetic Operations

41. Other Data Types
Chapter 4: Variables and Arithmetic Operations

42. Other Data Types
Chapter 4: Variables and Arithmetic Operations

43. Miscellaneous Data Types
Chapter 4: Variables and Arithmetic Operations

44. Variable Prefixes
Chapter 4: Variables and Arithmetic Operations

45. Literals
A value is called a literal when the value being used in the assignment statement is literally the value that is required
Chapter 4: Variables and Arithmetic Operations

46. Forced Literal Types
Sometimes you might want a literal to be a different data type than the Visual Basic default
Chapter 4: Variables and Arithmetic Operations

47. Constants
A constant variable will contain one permanent value throughout the execution of the program
Chapter 4: Variables and Arithmetic Operations

48. Constants
The declaration of a constant variable begins with the letters Const, not the letters Dim
You must assign the value to be contained in the constant on the same line as the definition of the constant.
You cannot attempt to change the value in the constant variable anywhere in the program. If you attempt this, you will produce a compiler error
The letter c often is placed before the prefix of the constant variable name to identify throughout the program that it is a constant variable and cannot be changed
Other than the letter c constant variable names are formed using the same rules and techniques as nonconstant names
Chapter 4: Variables and Arithmetic Operations

49. Referencing a Variable
When a variable is declared, it will be underlined with a green squiggly line until it is referenced in a statement
It is mandatory when using a variable in a program that the variable is defined prior to using the variable name in a statement
Chapter 4: Variables and Arithmetic Operations

50. Scope of Variables
The scope of a variable specifies where within the program the variable can be referenced in a Visual Basic statement
A variable can be referenced only within the region of the program where it is defined
The code between the Sub statement and the End Sub statement is a procedure
A variable that can only be referenced within the region of the program where it is defined is called a local variable
Local variables have a certain lifetime in the program
Global variables can be used in multiple regions of a program
Chapter 4: Variables and Arithmetic Operations

51. Converting Variable Data
Visual Basic includes several procedures that allow you to convert one data type to another data type
A procedure to convert a String data type to an Integer data type is named ToInt32
The procedure is found in the Convert class, which is available in a Visual Studio 2008 class library
Chapter 4: Variables and Arithmetic Operations

52. Using a Procedure
A procedure that performs its task but does not return a value is called a Sub procedure
A procedure that returns a value is called a Function procedure, or a function
An argument identifies a value required by a procedure
Every procedure is part of a class
Chapter 4: Variables and Arithmetic Operations

53. Using a Procedure
Chapter 4: Variables and Arithmetic Operations

54. Option Strict On
Visual Basic will, by default, automatically convert data types if the data type on the right side of the equal sign in an assignment statement is different from the data type on the left side of the equal sign
To prevent automatic conversion of values, the developer must insert the Option Strict On statement in the program prior to any event handler code in the program
The Option Strict On statement explicitly disallows any default data type conversions in which data loss would occur and any conversion between numeric types and strings
Chapter 4: Variables and Arithmetic Operations

55. Option Strict On
Chapter 4: Variables and Arithmetic Operations

56. Arithmetic Operations
Chapter 4: Variables and Arithmetic Operations

57. Arithmetic Operators
Chapter 4: Variables and Arithmetic Operations

58. Multiple Operations
A single assignment statement can contain multiple arithmetic operations
Hierarchy of Operations
Exponentiation (^) is performed first
Multiplication (*) and division (/) are performed next
Integer division (\) is next
MOD then occurs
Addition (+) and subtraction (-) are performed last
Within these five steps, calculations are performed left to right
Chapter 4: Variables and Arithmetic Operations

59. Displaying Numeric Output Data
Chapter 4: Variables and Arithmetic Operations

60. Format Specifications for the ToString Function
Use the format specifier to identify the format for the numeric data to be returned by the ToString function
Chapter 4: Variables and Arithmetic Operations

61. Precision Specifier
The precision specifier is a number that is included within the quotation marks in the function call to identify the number of positions to the right of the decimal point that should be returned
Chapter 4: Variables and Arithmetic Operations

62. Clear Procedure
The Clear procedure clears any data currently placed in the Text property of a TextBox object
Chapter 4: Variables and Arithmetic Operations

63. Clearing the Text Property of a Label
The Clear procedure cannot be used with a Label object
You must write an assignment statement that assigns a null length string to the Text property of a Label object
Chapter 4: Variables and Arithmetic Operations

64. Setting the Focus
When the focus is on a TextBox object, the insertion point is located in the text box
Chapter 4: Variables and Arithmetic Operations

65. Form Load Event
A form load event occurs when the program starts and the Digital Downloads form is loaded
This event handler completes the following tasks:
Display the cost per download heading
Clear the placeholder from the lblTotalCostOfDownloads Text property
Set the focus on the txtNumberOfDownloads text box
Chapter 4: Variables and Arithmetic Operations

66. Concatenation
The process of joining two different values into a single string is called concatenation
The values being concatenated must be String data types
Chapter 4: Variables and Arithmetic Operations

67. Concatenation
Chapter 4: Variables and Arithmetic Operations

68. Class Scope
When a variable is referenced in two different event handling procedures, it must be defined at the class level instead of the procedure (event handler) level
Chapter 4: Variables and Arithmetic Operations

69. Debugging Your Program
A Format Exception occurs when the user enters data that a statement within the program cannot process properly
Chapter 4: Variables and Arithmetic Operations

70. Debugging Your Program
An Overflow Exception occurs when the user enters a value greater than the maximum value that can be processed by the statement
It is not possible to divide by zero, so if your program contains a division operation and the divisor is equal to zero, the Divide By Zero Exception will occur
Chapter 4: Variables and Arithmetic Operations

71. Program Design
Chapter 4: Variables and Arithmetic Operations

72. Program Design
Chapter 4: Variables and Arithmetic Operations

73. Event Planning Document
Chapter 4: Variables and Arithmetic Operations

74. Summary Create, modify, and program a TextBox object
Use code to place data in the Text property of a Label object
Use the AcceptButton and CancelButton properties
Understand and declare String and Numeric variables
Use assignments statements to place data in variables
Chapter 4: Variables and Arithmetic Operations

75. Summary Use literals and constants in coding statements
Understand scope rules for variables
Convert string and numeric data
Understand and use arithmetic operators and arithmetic operations
Chapter 4: Variables and Arithmetic Operations

76. Summary Format and display numeric data as a string
Create a form load event
Create a concatenated string
Debug a program
Chapter 4: Variables and Arithmetic Operations

77. Variables and Arithmetic Operations
CHAPTER FOUR COMPLETE
Variables and Arithmetic Operations