1. IS 350 Numeric Data Types

2. Objectives Work with numeric data
Describe the difference between value types and reference types
Declare and use variables to store data
Create constants
Write expressions containing arithmetic operators and operands

3. Objectives (continued)
Convert data between numeric and String data types
Use the FV method
Use the TextBox control
Define the order in which control instances get input focus (Tab Order)

4. Introduction to Data Types
Every object and property has a data type
A data type defines what kind of data an object or property can store
Data types that store numbers are called numeric data types
Integral data types store whole numbers
Floating-point data types store values having a fractional part
Other data types store strings
Many other additional data types exist

5. Integral Data Types
Integral data types store data that does not have a decimal point
Some integral data types can store 0 or positive values
Other integral data types can store both positive and negative values
Negative values are indicated by a sign bit

6. Integral data types

7. Integral Data Types Integral values are stored as binary numbers
The SByte data type stores its data in 8 bits
7 bits store the data
1 bit stores the value's sign
The largest possible value is 2^7-1 or 127
The value has the binary pattern

8. Floating-point Data Types
Floating-point numbers store values with a decimal point
Floating-point numbers are stored in a form of scientific notation
One bit is the sign bit
A 23-bit mantissa stores the fractional part of a number
The exponent is stored in 8 bits

9. Floating-point data types

10. Rounding Errors
Floating-point numbers are an approximation of an actual value
1/3 or 2/3 must be rounded, for example
Rounding introduces an error called rounding error
The greater the precision of the data type, the smaller the rounding error
The Decimal data type has the smallest rounding error and the greatest precision

11. Performance of Numeric Data Types
Performance is a key characteristic of any application
Different data types have different performance characteristics
Arithmetic operations using integral data types is faster than operations on floating-point data types
The Decimal data type is very slow
Decimal prevents rounding error

12. Properties of Numeric Data Types
Numeric data types have constant fields that store the minimum and maximum possible values for the data type
MinValue stores the minimum possible value
MaxValue stores the maximum possible value
Primary data types are structures having constant values

13. Introduction to the String Data Type
Data is often represented as a string of characters
Textual data is represented as a string
Data entered by end users is textual
Strings are used to display output
Strings are represented differently than numbers (numeric data types)
Much more later

14. Storage of the String Data Type
Strings are stored as Unicode characters in two bytes as an unsigned short (UShort)
The first 127 values store letters, digits, and special characters
Values 128 to 255 store special characters such as keyboard arrows
Values 256 to 65,535 store international characters and diacritical marks

15. Introduction to Value Types and Reference Types
A data type can be characterized as a value type or reference type
Value types store data in the memory allocated to the variable
Reference types store a 32-bit memory address
The memory address points to the actual object

16. Value Types All value types derive from the System.ValueType class
Integral and floating-point data types are value types
Dates and times are value types
Structures are value types

17. Storage of value types

18. Reference Types All reference type variables are 32 bits in size
The value stored in a reference type variable is a memory address
This memory address points to the memory allocated to the actual data
The term pointer is often used to describe a reference type

19. Storage of reference types

20. Introduction to Variables
A variable stores data while an application runs
The process of creating a variable is called declaring a variable
A variable has a name (identifier)
Naming rules for variables and procedures are the same
A variable has a data type

21. Variable Characteristics
All variables have three characteristics
Lifetime
Scope
Accessibility

22. Variable Lifetime
Variable lifetime refers to the period of time that a variable exists
A variable having local lifetime exists only while a procedure executes
A variable with a module-level lifetime exists while a class instance exists or a module is loaded

23. Variable Scope and Accessibility
Variable scope refers to the statements that can use a variable
Variables declared inside a procedure with the Dim statement have local scope
Variables declared outside a procedure with the Private statement have module-level scope

24. Variable Declaration Syntax
[Dim] varName As type [= initexpr]
Dim keyword declares a local variable
The variable and its value are destroyed when the procedure ends
varName contains the name (identifier) of the variable
type defines the variable’s data type
Optional initexpr is initializes the variable’s value

25. Declaring a Local Variable (example)
Declare a local variable named Total having the Double data type
Sub Main()
Dim Total As Double
End Sub 25

26. Initializing Variables
Variables can be declared and initialized in the same statement
Example:
Declare a variable named CurrentYear and initialize it’s value to 2010:
Dim CurrentYear As Integer = 2010

27. Common Initialization Errors
Numeric initialization values cannot contain formatting characters
The following statements are illegal:
Dim Value1 As Double = 100,000.52
Dim Value2 As Double = $100,000.52

28. Declaring Multiple Variables in One Statement
Multiple variables can be declared in the same statement
Separate each declaration with a comma as follows:
Dim IntegerValue As Integer, DoubleValue As Double
If variables have the same data type, use the following shorthand notation:
Dim IntegerValue1, IntegerValue2 As Integer

29. Variable Naming Conventions
A scheme of naming variables is called a naming convention
Naming conventions improve a program’s readability
Common naming conventions
Hungarian notation
Pascal case
Camel case

30. Naming Conventions (description)
Hungarian notation:
Use a prefix to denote the data type followed by a descriptive name
Pascal case
Use whole words
Capitalize the first letter of each word
Camel case
Use lower case for the first letter of the first word
Capitalize the first letter of each remaining word

31. Introduction to Constants
Constants are similar to variables
The value of a constant does not change while an application runs
Trying to assign a value to a constant will cause an error
Use the Const statement to declare a constant
Constants are typically declared at the module-level

32. User-defined Constant (example)
Declare a constant to store the value of PI
Private Const PI_VALUE As Single _ =
Declare a constant to store the value of PI multiplied by 2
Private Const TWO_PI_VALUE As Single _
= PI_VALUE * 2

33. Introduction to Expressions
Variables can be used in assignment statements along with object properties
Examples:
Dim Result As Integer
Dim Example As Integer = 4
Result = 3 ' Literal value
Result = txtExample.Height ' Property
Result = Example ' Another variable

34. Common Expression Errors
Values on the right and left sides of an assignment statement must have the same data type
The Font and Integer data types are not compatible so the following statements will cause an error:
Dim SomeInteger As Integer
SomeInteger = txtExample.Font

35. Parts of an Expression Operators Operands
Arithmetic operators such as (+, -, *, /, ^, \)
Comparison and logical operators
Operands
Literal values
Object properties
Constants
Variables

36. Operator Precedence
Operators have an evaluation order called precedence
Visual Basic precedence rules are the same as algebraic precedence rules
Use parentheses to override the default precedence rules
Use parentheses to clarify evaluation order
Extra parentheses do no harm

37. Operators and Precedence
Programming with Microsoft Visual Basic 2008: An Object-Oriented Approach, Third Edition

38. Arithmetic Operators (example)
Divide 10 by 5 and multiply the intermediate result by 100
The value 200 is stored in Result
Dim Numerator As Double = 10
Dim Denominator As Double = 5
Dim Result As Double
Result = Numerator / Denominator * 100

39. Integer Division
The result of an Integer division operation is an integral value
The result is truncated rather than rounded
Examples:
Result = 4 \ 3 ' > 1
Result = 5 \ 2 ' > 2
Result = 14 \ 4 ' > 3

40. The Mod Operator
Mod operator calculates the Integer remainder of a division operation
The operation is the same as the remainder resulting from a long division operation
Examples:
Result = 4 Mod 3 ' Remainder is 1
Result = 14 Mod 4 ' Remainder is 2

41. Operator Precedence
Arithmetic operators are applied in a default order known as precedence
Exponentiation
Multiplication and division
Integer division
Mod operator
Addition and subtraction
Use parentheses to change the default precedence

42. Numeric Data Types and Type Conversion
Type conversion is used to convert data from one data type to another
How type conversion is performed depends on whether strict type checking is enabled or disabled
If strict type checking is enabled, less restrictive types will not be implicitly converted to more restrictive types
Strings will not be implicitly converted to numeric data types

43. Introduction to Strict Type Checking
Widening type coercion allows more restrictive types to be implicitly converted to less restrictive types
Integral data types will be converted to floating-point types
Short to Integer is legal
Integer to Single is legal
Single to Double is legal
Double to Integer is not legal
Integer to Short is not legal

44. Enabling Strict Type Checking
Enable strict type checking to prevent hard to find type conversion errors
Option Strict statement enables or disables strict type checking
Option Strict statement must appear at the beginning of a module
Example:
Option Strict On ' Enable
Option Strict Off ' Disable

45. Explicit Type Conversion Methods
ToInt16, ToInt32, and ToInt64 convert the argument to an integral value
ToDecimal converts the argument to the Decimal data type
ToDouble and ToSingle convert the argument to floating-point data
ToString converts the argument to a string

46. Performing Explicit Type Conversion
Members of the System.Convert class explicitly convert data from one type to another
Methods exist for each primary data type
Example:
Dim DoubleValue As Double =
Dim IntegerResult As Integer
IntegerResult = _ System.Convert.ToInt32(DoubleValue)

47. Formatting Output Strings
The ToString method accepts an argument to format numeric data
Named formats supply common formatting actions
Currency and Percent for example
Custom formats are created with placeholder characters

48. Format specifiers

49. Placeholder characters

50. The Imports Statement
Use the Imports statement to eliminate fully qualified references to method names
The Imports statement appears after the Option Explicit and Option Strict statements
It’s possible to import any number of namespaces or classes
The order in which Imports statements appear is not significant
Types can also be imported using the Project Properties dialog box

51. Imports Statement (example)
Import the System.Convert class
Option Explicit On
Option Strict On
Imports System.Convert
Public Class frmMain
' statements
End Class

52. The FV Method and Intrinsic Function
The FV function calculates the future value of an investment
Arguments:
First argument contains the interest rate
Second argument contains the number of periods
Third argument contains the amount of the periodic payment
Optional fourth argument contains the present (initial) value of the investment
Optional fifth argument defines whether payments are made at the beginning or end of the period

53. The FV Function (Example)
Calculate the future value of $1, for 12 periods at 1% per period
Dim MonthRate As Integer = 0.01
Dim MonthTerm As Integer = 12
Dim InitialValue As Single =
Dim FutureValue As Double
FutureValue = FV(0.01, 12, 0, 1000)
FutureValue = FV(MonthRate, MonthTerm, 0, _
InitialValue) ' -1,

54. The TextBox Control (Introduction)
The TextBox control gets input and displays output
The control derives from the TextBoxBase class
Other textual controls include the MaskedTextBox and RichTextBox controls

55. The TextBox Control (properties)
BorderStyle - defines the style of the border
ForeColor and BackColor - define text and background colors
Enabled - defines whether the control instance can get input focus
ReadOnly - controls whether the text in the control instance can be copied to the clipboard
MultiLine - defines whether text will appear on multiple lines
MaxLength - defines the maximum number of characters

56. The TextBox Control (properties continued)
ScrollBars - defines whether scroll bars appear
Scroll bars only appear when the MultiLine property is True
Text - stores the visible text
TextAlign - defines how text is aligned in the control instance
The size and position is defined by the X, Y, Height and Width properties

57. The TextBox Control (Methods and Events)
Focus - used to set input focus to a text box
Enter - fires when the control instance gets focus
Leave - fires when the control instance loses focus

58. Introduction to Tab Order
Every form has exactly one active control instance at run time
This is the control instance having input focus
The order in which control instances get focus is called the tab order
tab order is set using the TabIndex property
tab order can also be set using a visual designer