Chapter 4 — Variables and Arithmetic Operations
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Transcript of Chapter 4 — Variables and Arithmetic Operations
CHAPTER FOURVariables and
Arithmetic Operations
Chapter 4: Variables and Arithmetic Operations 2
Objectives
Create, modify, and program a TextBox object
Use code to place data in Text property on Label object
Use the AcceptButton and CancelButton properties
Understand and declare String and Numeric variables
Use assignments statements to place data in variables
Use literals and constants in coding statements
Chapter 4: Variables and Arithmetic Operations 3
Objectives
Understand scope rules for variables
Convert string and numeric data
Understand & use arithmetic operators & arithmetic
operations 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 4
Introduction
Chapter 4: Variables and Arithmetic Operations 5
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
Chapter 4: Variables and Arithmetic Operations 6
TextBox Objects
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 7
Sizing and Positioning a TextBox Object
Enter txtNumberOfDownload into the Name property of the
TextBox
Scroll to the Text property and click the right column of the Text
property
Type the maximum number of characters the user normally will
enter into the text box and then press the ENTER key. Use the
digit 8 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 8
Sizing and Positioning a TextBox Object
Drag the right edge of the TextBox object to resize the
TextBox object so it is slightly wider than an 888 entry
Scroll to the Font property to change font to Century
Gothic and the font size to 12.
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 9
Sizing and Positioning a TextBox Object
Chapter 4: Variables and Arithmetic Operations 10
Aligning Text in a TextBox Object
Scroll to the TextAlign property of the Text box
Click the TextAlign property in the left column, and
then click the list arrow in the right
Click Center in the TextAlign property list
Chapter 4: Variables and Arithmetic Operations 11
Aligning Text in a TextBox Object
Chapter 4: Variables and Arithmetic Operations 12
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 13
Creating a MaskedTextBox Object
Chapter 4: Variables and Arithmetic Operations 14
Creating a MaskedTextBox Object
Drag a MaskedTextBox 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
Chapter 4: Variables and Arithmetic Operations 15
Creating a MaskedTextBox Object
Chapter 4: Variables and Arithmetic Operations 16
Label Objects
Drag a Label object to the 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 17
Label Objects
Chapter 4: Variables and Arithmetic Operations 18
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 ENTER
Click a blank area in the Windows
Scroll to and select the AcceptButton Properties.
Click the AcceptButton property list arrow in the right
column
Click btnCalculateCost in the AcceptButton property list
Chapter 4: Variables and Arithmetic Operations 19
Accept Button in Form Properties
Chapter 4: Variables and Arithmetic Operations 20
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 21
String Data Type
A String variable allows any character 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 22
String Data Type
Chapter 4: Variables and Arithmetic Operations 23
Assignment Statements
One method to place data in the variable is to use an assignment statement
Chapter 4: Variables and Arithmetic Operations 24
Assignment Statements
In the code editing window type Dim followed by a space.
Then, type 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 25
Assignment Statements
Type strn. IntelliSense displays the 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 txt to display the IntelliSense list of the Form objects, and then type n to identify the txtNumberof Downloads Text Box 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 26
Assignment Statements
Chapter 4: Variables and Arithmetic Operations 27
Numeric Data Types
A numeric data type must be used in arithmetic operations
Chapter 4: Variables and Arithmetic Operations 28
Numeric Data Types
Chapter 4: Variables and Arithmetic Operations 29
Other Data Types
Chapter 4: Variables and Arithmetic Operations 30
Other Data Types
Chapter 4: Variables and Arithmetic Operations 31
Miscellaneous Data Types
Chapter 4: Variables and Arithmetic Operations 32
Variable Prefixes
Chapter 4: Variables and Arithmetic Operations 33
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 34
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 35
Constants
A constant variable will contain one permanent value throughout the execution of the program
Chapter 4: Variables and Arithmetic Operations 36
Constants
Constant variable the definitions begins with the letters Const, not the
letters Dim
The value of the constant must be on the same line as the definition of
the constant.
At run time, you cannot attempt to change a constant variable value.
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 us the same naming
convention
Chapter 4: Variables and Arithmetic Operations 37
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 in a statement
Chapter 4: Variables and Arithmetic Operations 38
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
Chapter 4: Variables and Arithmetic Operations 39
Scope of Variables (Continued)
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 40
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 2010 class library
Chapter 4: Variables and Arithmetic Operations 41
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 42
Using a Procedure
Chapter 4: Variables and Arithmetic Operations 43
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
Chapter 4: Variables and Arithmetic Operations 44
Option Strict On
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 45
Arithmetic Operations
Chapter 4: Variables and Arithmetic Operations 46
Arithmetic Operators
Chapter 4: Variables and Arithmetic Operations 47
Multiple Operations(Order of Operations)
A single assignment statement can contain multiple 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 48
Displaying Numeric Output Data
Chapter 4: Variables and Arithmetic Operations 49
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 50
Precision Specifier
The precision specifier is a number that is included within 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 51
Clear Procedure
The Clear procedure clears any data currently placed in the Text property of a TextBox object
Chapter 4: Variables and Arithmetic Operations 52
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 53
Setting the Focus
When the focus is on a TextBox object, the insertion point is located in the text box, and will be blinking
Chapter 4: Variables and Arithmetic Operations 54
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 55
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 56
Concatenation
Chapter 4: Variables and Arithmetic Operations 57
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 58
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 59
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 60
Program Design
Chapter 4: Variables and Arithmetic Operations 61
Program Design
Chapter 4: Variables and Arithmetic Operations 62
Event Planning Document
Chapter 4: Variables and Arithmetic Operations 63
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
Use literals and constants in coding statements
Chapter 4: Variables and Arithmetic Operations 64
Summary
Understand scope rules for variables
Convert string and numeric data
Understand and use arithmetic operators and operations
Format and display numeric data as a string
Create a form load event
Create a concatenated string
Debug a program
CHAPTER FOUR COMPLETEVariables and
Arithmetic Operations