1. Introduction to Tools, Numeric Data Types and Variables
Chapter 3
Introduction to Tools, Numeric Data Types and Variables

2. Objectives
Create a text box for input and output and define an accept and cancel button for a form
Define the order in which the user navigates from one control instance to another by pressing the Tab key
Explicitly set input focus and create ToolTips for control instances
Create variables to store information while a solution runs
Understand the organization of namespaces

3. Objectives Learn how to create comments
Understand the events that occur as a user navigates between text boxes
Perform computations with variables using assignment statements
Understand the role of precedence, perform type conversions, and format data
Write a statement on multiple lines and calculate solution output

4. The Text Box Control
Used to display output to the user and get text input from the user
Similar to a Label control but a Label control only displays output
Standard prefix for a text box is "txt"
User enters text into one text box at a time
This text box is said to have input focus or focus

5. TextBox Control – Properties
BorderStyle - defines the border surrounding the text box
ForeColor, BackColor - defines the text color and background color respectively
Enabled - controls whether the text box can get focus and will respond to events
Locked - controls whether user can change the text appearing in the text box
MultiLine - controls whether text will appear on multiple lines
MaxLength - defines the maximum number of characters that the user can enter into the text box

6. TextBox Control – Properties
Name - defines name used to reference control instance with code
Again, use a standard prefix of "txt"
ScrollBars - defines whether vertical or horizontal scroll bars appear in text box
Text - contains the text appearing in text box
TextAlign - justifies text within the visible region of the control instance
X, Y, Height, Width properties define the position and size of the control instance

7. TextBox - Methods and Events
Focus method sets input focus to a text box
Enter event fires when text box gets focus
Leave event fires when text box loses focus
TextChanged event fires when the changes the textual contents at run time
The event fires for each character typed

8. AcceptButton & CancelButton Properties
One button on a form can be designated as the accept button and another the cancel button
Set the form’s AcceptButton property to a Button control instance to define the accept button
Click event handler executes when user presses the Enter key
Set the form’s CancelButton property to Button control instance to define the cancel button
Click event handler executes when user presses the Esc key

9. Setting the Tab Order
Order in which control instances get focus is called the tab order
The TabIndex property defines tab order
Set the TabIndex property to a unique Integer value for each control instance that can get focus

10. Setting the Tab Order To set the tab order visually
Activate the Win Form Designer
On the menu bar, click View, and then click Tab Order
Click the control instances in the order that you want them to get focus
Click View, and then click Tab Order again to record your changes

11. Setting the Tab Order
Tab order of control instances appear in upper-left corner of control instance region

12. Explicitly Setting Input Focus
Call the Focus method of a text box or other object that can get input focus
Set the input focus to the text box named txtInitialValue
txtInitialValue.Focus()

13. ToolTips
ToolTips appear as a pop-up when the mouse hovers over a control instance for a short period
Standard prefix is "tip"
InitialDelay property defines the time interval for mouse to hover before the ToolTip appears
AutomaticDelay property defines the amount of time that the ToolTip appears
After creating the ToolTip, set the ToolTip on control property for each control instance
Note that the control instance appears in resizable tray below the form because it is not visible at run time

14. ToolTips (Example) ToolTip on TipGeneral Property
ToolTip control instance

15. Storing Data in Variables
Variable stores data while a solution runs
A variable is simply a unique name that identifies a space in memory (RAM)
Data may be a string of characters or a number
Every variable has a data type
A variable's data type determines the kind of information that the variable can store
Numbers, characters, etc.
Every variable has a name
Use standard prefixes for variable names to denote data type

16. Numeric VB .NET Data Types
Storage Size
Prefix
Possible Values
Boolean
2 bytes
bln
True or False
Date
8 bytes
dat
Dates between 1/1/0001 and 12/31/9999
Short
sho
Positive and negative whole numbers between –32768 and 32767
Integer
4 bytes
int
Positive and negative whole numbers between –2,147,483,648 and 2,147,483,647
Long
lng
Positive and negative whole numbers

17. Numeric VB .NET Data Types
Storage Size
Prefix
Possible Values
Single
4 bytes
sng
A number with at most 6 digits to the right of the decimal point
Double
8 bytes
dbl
A number with at most 14 digits to the right of the decimal point
String
1 byte per character
str
Character string of up to about 2 billion characters

18. Standards for Variable Names
Use a one-character prefix to denote scope
The scope of a variable indicates which event handlers can use that variable
Use a three-character prefix to denote data type
Add an additional prefix character to denote a variable's scope
Module-level variables carry a prefix of "m"

19. Standards for Variable Names
Valid Variable Name
Invalid Variable Name
Cause
mlngCounter
mlng.Counter
A period (.)
mintTotal
mint Total
A space
mdblFutureValue
mdlbFuture-Value
A dash (-)
mdblGain
mdbl*Gain
Special characters

20. Declaring a Variable Private statement declares variable
Private varname As type [ = initialization expression]
varname is variable name
As type contains data type of variable
Optional initialization expression contains the initial value of a variable
Example: Declare variables having the Double and Integer data types
Private mdblInterestRate As Double
Private mintCounter As Integer

21. Declaring a Variable Initialize a variable when declaring it
New to VB .NET
Example: Declare a modular Integer variable and store the value 30 in the variable
Private mintYearTerm As Integer = 30
Focus (m)
Prefix (int)
Name YearTerm

22. Declaring a Variable
Do not include punctuation characters in a variable initialization
The following declarations are illegal because of the $ sign and commas:
Private mdblInitialValue As Double = 100,000.52
Private mdblInitialValue As Double = $100,000.52
Possible to declare multiple variables on the same line
Private mintYearTerm, mintMonthTerm As Integer

23. Declaring Module-Level Variables
Declare module-level variables after the statements generated by the Window Form Designer but outside an event handler

24. What is a namespace?
Namespaces are a way to define the classes and other types of information into one hierarchical structure.
System is the basic namespace used by every .NET code. If we can explore the System namespace little bit, we can see it has lot of namespace using the system namespace. For example, System.Io, System.Net, System.Collections, System.Threading, etc.

25. The Organization of Namespaces
VB .NET accesses predefined components via namespaces
Namespaces developed by .NET teams begin with System
Namespaces developed by others at Microsoft begin with Microsoft
Namespaces are organized hierarchically

26. The Organization of Namespaces
System namespace
System
Drawing namespace
System.Drawing
Windows.Forms namespace
System.Windows.Forms
Data namespace
System.Data
Printing namespace
System.Drawing.Printing

27. Parts of a Namespace A namespace contains:
Enumerations which define a symbolic name for a value
Classes which are reference types
Structures which are value types

28. Windows.Forms namespace System.Windows.Forms
Parts of a Namespace
Windows.Forms namespace System.Windows.Forms
Classes
Structures
Enumerations
Button
Message
BorderStyle
Label
FormBorderStyle
TextBox

29. Namespace Enumerations
Enumerations define a symbolic name for a value
Enumerations improve code readability
The BorderStyle enumeration applies to the System.Windows.Forms namespace
lblFileName.BorderStyle = _ System.Windows.Forms.BorderStyle.FixedSingle
Namespace
Property
Enumeration

30. Namespace Classes Classes are reference types
Variable stores the memory address of an object rather than the object itself
Controls appearing in the Toolbox are all classes
Variable btnCalculate
023448
Variable contains memory address of Button control instance
btnCalculate (name)
(Memory address )
Data
btnCalculate.text = "Calculate" …

31. Namespace Structures Structures are value types
Store data directly in the variable
Primary data types such as Boolean, Integer, Single, and Double are all “Structures”
Note that the String data type is a class though
We will discuss strings separately

32. Creating Well-Written Comments
A Comment is a full or partial line of text ignored by VB .NET
Create comments to describe what your code is doing or how code performs a particular task
Multiple comments are called a comment block
Blank lines between statements are ignored and are called whitespace
A comment can appear on its own line and begins with a single quote ( ' )
A comment can appear at the end of a line

33. Creating Well-Written Comments
The following is a comment appearing on its own line:
' This line is a comment.
The following comment appears at the end of a line. Note a space must precede the comment character
txtDemo.text = "Dog" 'Store "Dog" in the text box
Comment

34. Creating Well-Written Comments
VB .NET displays comments in in green

35. Writing Assignment Statements Using Variables
Store a property in a variable
mintResult = txtExample.Height
Store a literal value in a variable
mintResult = 3
Store another variable in a variable
mintResult = mintExample

36. This is also called an assignment statement
Arithmetic Operators
Expressions consists of literal values, constants, variables and arithmetic operators
An arithmetic operator performs a mathematical calculation
Multiply the literal values 3 and 2 together and store the result (6) in the variable mintResult
mintResult = 3 * 2
This is also called an assignment statement

37. Arithmetic Operators (2)
Operators in Order of Precedence
Description
Example ^
Raises a number to the power of an exponent
2 ^ 3 is equal to 8
* /
Multiplication and Division
2 * 3 is equal to 6
8 / 4 is equal to 2 \
Integer Division
10 \ 3 is equal to 3
5 \ 2 is equal to 2
Mod
Modulus arithmetic
10 Mod 3 is equal to 1
+ -
Addition and subtraction
2 + 3 is equal to 5

38. Arithmetic Operators – Example
Divide two numbers and multiply the intermediate result by 100
Private mdblNumerator As Double = 10
Private mdblDenominator As Double = 5
Private mdblResult As Double
mdblResult = mdblNumerator / mdblDenominator * 100

39. The Role of Precedence
Programming languages evaluate arithmetic expressions from left to right in a predefined order known as precedence
Perform exponentiation first
Next perform multiplication and division
Next perform Integer division and then apply the Mod operator
Next perform addition and subtraction
Parenthesis override default precedence
Parenthesis may be nested

40. (Var1 + Var2) / (Var3 + Var4) * (Var5 ^ Var6)
Precedence (Example)
(Var1 + Var2) / (Var3 + Var4) * (Var5 ^ Var6)
1 (addition)
2 (addition)
3 (exponent)
4 (division)
5 (multiplication)

41. Type Conversion
VB .NET must convert data from one data type to another when evaluating mathematical expressions
The Option Strict On statement enables strict type checking
Strict type checking requires explicit type conversion from less restrictive types to more restrictive types
Use strict type checking to minimize hard to find errors resulting from implicit type conversion

42. Strict Type Checking (Example)
The following statement will cause an error if strict type checking is enabled. If disabled, mintPI will store the value 3
Note that the result if the implicit type conversion is truncation
Private mintPI As Integer =

43. Option Explicit
Option Explicit On statement requires that you declare variables before using them the first time
Also reduces hard to find errors resulting from typos
Note that Option Explicit and Option Strict statements appear at the beginning of a module

44. Type Conversion Methods
Methods belong to the System.Convert class
ToInt16 converts value to a Short
ToInt32 converts value to an Integer
ToInt64 converts value to a Long
ToDouble converts value to a Double
ToSingle converts value to a Single
ToString converts value to a String
Each method takes one argument; the value to convert
Note that these methods supercede older intrinsic functions like CInt and CLng

45. Type Conversion Examples
Private msngInput As Single = 3.44
Private mstrInput As String = "3.95“ ‘ why use “”
Private mintOutput As Integer
Private msngOutput As Single
Convert a Single to an Integer
mintOutput = System.Convert.ToInt32(msngInput)
Convert a String to an Integer
mintOutput = System.Convert.ToInt32(mstrInput)
Convert a String to a Single
msngOutput = System.Convert.ToSingle(mstrInput)

46. Numeric Overflow
Numeric overflow occurs when trying to store too large a number in a variable
The following statements will cause a numeric overflow error because the largest number that can be stored in a short is 32767
Private mshoExample As Short
mshoExample = 46000
mshoExample = 2500 * 2500

47. Numeric Overflow
VB .NET performs arithmetic using less restrictive type on right side of expression
The last statement will cause numeric overflow:
Private mshoArg1 As Short, mshoArg2 As Short
Private mintArg3 As Integer
mshoArg1 = 32000
mshoArg2 = 32000
mintArg3 = mshoArg1 * mshoArg2

48. Formatting a Numeric Value with Methods
The ToString type conversion method accepts a string argument to format data
Special characters are used to define the format
lblGain.Text = mdblGain.ToString("$##,###.##")
variable
ToString method
argument defines how to format the value

49. Formatting Placeholders
Character
Description
Digit placeholder. If number corresponding to position does not contain a value, then a 0 appears #
Digit placeholder. If number corresponding to position does not contain a value, then a space appears .
Decimal placeholder. Defines the position of the decimal point ,
Thousands separator %
Percentage placeholder
- + $ ( )
Literal characters embedded in the format string

50. Formatting Examples Format String (Mask) Value Formatted value
123.45
###,###.00
1234.4
1,234.40
$###,###.00
$1,234.40
###%
0.08 8%
##.00%
8.00% C $ F

51. Continuation Lines Use when statement will not fit on a line
Underscore (_) is the continuation character
Rules for use
A Space (⇑) must precede the continuation character
You cannot follow a continuation character with a Comment
Do not break up words
Multiple continuation lines allowed

52. Continuation Lines (Example)
The following statement appears on two lines:
mdblInterestRate =⇑_
System.Convert.ToDouble(txtInterestRate.Text) / 100