Chapter 3: Introducing the
Microsoft .NET Framework
and Visual Basic .NET
Visual Basic .NET Programming:
From Problem Analysis to Program Design
Exploring the Microsoft .NET
Framework
• .NET Framework key parts:
– Compilers for:
• VB .NET
• Other supported .NET languages
– Common Language Runtime (CLR) – translates files from
the compilers into executable files
– Framework Class Library (FCL) – contains hundreds of
prewritten classes
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Visual Basic .NET Programming: From Problem Analysis to Program Design
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The Microsoft .NET Compilers
• Compiler has two primary purposes:
– Check source code for syntax errors
– Translate it into executable form
• Compilers translate source code into code, which
could be understood by the Common Language
Runtime (CLR) and then executed by the
computer
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The Framework Class Library
• Consists of over 100 classes (a class defines what all
objects of a group have in common)
• Files have suffix of .dll
• Namespaces
– Organize classes
– Can contain both classes and other namespaces
– Compilers do not automatically search all namespaces
for classes used by code
• Must use keyword Imports
• Tell compiler specific namespaces to access
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Visual Basic .NET Programming: From Problem Analysis to Program Design
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Writing a Visual Basic .NET
Module Definition
• Module definition
– Begins with keyword Module
– Ends with keyword End Module
• Statements contain:
– Keywords: Module, Sub, End Sub, etc.
– Identifiers: Main, firstName, number1, etc.
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Writing a Visual Basic .NET
Module Definition (continued)
• Identifier
– Name assigned to things such as:
• Modules
• Procedures
• Variables
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Writing a Visual Basic .NET
Module Definition (continued)
• Identifier naming rules:
– Can be up to 1023 characters long
– Can include any:
•
•
•
•
Letter
Number
Underscore character
No spaces
– Cannot begin with a number
– Cannot be a keyword
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Writing a Visual Basic .NET
Module Definition (continued)
• Code not case sensitive
• Comment lines (e.g. ‘this is a comment)
– Add explanations to code
– Ignored by compiler
• Module header
– Names module
– Syntax:
• Module modulename
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Writing a Visual Basic .NET
Module Definition (continued)
• Procedure:
– Contains statements that perform processing
– Types:
• Sub – does not return a value
• Function – returns a value
– Begin with header
• Procedure Main invoked automatically
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Writing a Visual Basic .NET
Module Definition (continued)
• Argument
– Information contained in parentheses when calling
procedure (e.g. Console.Write(“argument”))
– Passed to procedure
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Defining Visual Basic .NET
Variables And Data Types
• Variable
– Memory location that contains data
– Characteristics:
• Name
• Data type
• Value
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Understanding VB .NET Data
Types
• Each variable has a data type
• Can be:
– Primitive
– Complex
• The computer allocates two bytes for each
character and accommodates all characters of
major international languages
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Declaring and Populating
Variables
• Declaration statements
– Define variables
• Syntax:
– Dim variablename As datatype
• Assignment operator
–=
– Assigns value on right side to variable named on
left side
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Examples
• Declaring Variables:
Dim myInteger As Integer
Dim myDouble As Double
Dim myBoolean As Boolean
• Populating Variables
myInteger = 1
myDouble = 2.5
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Defining Constants
• Constant
– Variable with a value that does not change
– Contain values such as:
• Company name
• Tax identification number
– Syntax:
• Const constantname As datatype
– Must be initialized in the same statement that
declares it
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Defining Constants (continued)
• Naming convention:
– Capitalize constant names
– If name consists of more than one word
• Separate words with underscore character (_)
– Example:
• TAX_ID
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Module Module1
Sub Main()
'declare variables
Dim exam_Score1, exam_Score2 As Integer
Dim average As Double
Dim studentCSIT108 As Boolean
'declare a constant
Const PI As Double = 3.14
'populate variables
exam_Score1 = 86
exam_Score2 = 96
'compute average score
average = (exam_Score1 + exam_Score2) / 2
'display result
Console.WriteLine("the average is: " & average)
Console.WriteLine()
End Sub
End Module
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Converting Data Types
• Numeric data types have different capacities:
– Byte variable can hold maximum value of 255
– Integer variable has maximum value of 2.1 billion
• Implicit type conversion
– Use assignment operator to assign contents of
variable to a variable with different data type
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Example 3-7: Implicit Type
Conversion
Dim myInteger As Integer = 1
Dim myDouble As Double = 2.5
myDouble = myInteger
• Assign Integer value to Double variable
– Data type Double has greater capacity than Integer
– No potential loss of data
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Example 3-8: Loss of Precision
• Loss of precision
– Computing error that can occur when decimal
positions are dropped
Dim myInteger As Integer = 1
Dim myDouble As Double = 2.5
myInteger = myDouble
DO NOT DO THIS
• VB .NET will automatically round decimal
values before truncating (cutting)
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Example 3-8: Loss of Precision
(continued)
• Option Strict
– Prevent unintentional loss of precision when
mixing data types in assignment statements
– Compiler detects potential loss of precision
• Displays error message
• Explicit type conversion
– Invoke Convert method to convert data types
Do ex. 3-9, p. 96
Do ex. 3-11, p. 98 & Read p. 100
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Module Module1
Sub Main()
'declare variables
Dim numDouble as Double
Dim numInt as Integer
'populate variables
numDouble = 119.6
numInt = 119.6
‘display result: the integer number is rounded up
Console.WriteLine("integer: " & numInt)
Console.WriteLine("double: " & numDouble)
‘display result: the integer number is rounded up
numDouble = 11.634
numInt = NumDouble
Console.WriteLine(“After assigning a decimal number/value to an
integer variable, the integer variable contains " & numInt & “ ; the number
assigned to it was “ & numDouble)
End Sub
End Module
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Converting Data Types
(continued)
• Option Explicit
– Must define variable before using it in a statement
– Otherwise
• Compiler generates error message
– Generally set On
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Using Reference Variables
• Uses class name as data type
• For example:
– String
• Variable refers to or points to instance of class
– Does not actually contain data
– Contains memory address of instance of class that
contains data
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Using the Arithmetic Operators
• Arithmetic operators
– For multiplication, division, addition, and subtraction
– *, /, +, • Evaluated in predetermined order called precedence
– Standard algebraic rules of precedence apply (p. 101)
• Other operators:
– Exponentiation
– Integer division
– Remainder computation
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Example 3-15:
Integer Division (\)
Dim firstInt As Integer
Dim secondInt As Integer
Dim integerResult As Integer = 0
firstInt = 11
secondInt = 2
integerResult = firstInt \ secondInt
Console.WriteLine(“integerResult = firstInt \
secondInt: “ & integerResult)
• Result: 5, not 5.5
Do ex. 3-13 & 3-14, p.102
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Using the Arithmetic Operators
(continued)
• Assignment operators:
– Formed by combining 1 of the arithmetic operators
with the assignment operator
– Example:
• i += 1 is the same as i = i + 1
See table 3-6, p. 105
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Invoking Methods in the Math
Class
• System namespace includes Math class
– Contains methods to accomplish
• Exponentiation
• Rounding
• Trigonometric calculations
See table 3-7, p. 105
• To invoke (use) a method from the class library:
– Use word “Imports” is necessary
– Syntax: ClassName.MethodName(argument)
• Math.Pow(firstInt, secondInt)
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Invoking Methods in the Math
Class (continued)
• Math class constants:
– PI and E (exponent)
– To access:
• Math.PI
Do ex. 3-18, 3-19, 3-20, p. 106
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Reading Input From the
Keyboard
• Use Console class (part of the System namespace)
– ReadLine method: Console.ReadLine()
• Read one or more characters from keyboard
• Convert any numeric data to desired data type
• Prompt
– Message displayed to user asking for input
Do ex. 3-21, p. 108
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Programming Example:
Temperature Converter
• Input
– Fahrenheit temperature including decimal positions
• Output
– Celsius temperature that corresponds to Fahrenheit
temperature that was input
• Results rounded to one decimal position
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Programming Example:
Temperature Converter
(continued)
• Main Algorithm
– Declare variables
– Prompt user for input
– Invoke Console.ReadLine to input value from
keyboard
– Invoke Convert.ToDouble to convert data type
String to Double
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Programming Example:
Temperature Converter
(continued)
• Main Algorithm (continued)
– Compute Celsius temperature
– Invoke Math.Round to round computed value to
one decimal position
– Invoke Console.WriteLine to display rounded
Celsius temperature
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Summary
• Framework consists of:
– Compilers
– Common Language Runtime (CLR)
– Framework Class Library (FCL)
• VB .NET statements consist of
– Keywords
– Identifiers
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Summary (continued)
• Modules
• Procedures:
– Subs
– Functions
– Procedure Main invoked automatically
• Variable:
– Memory location that contains data
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Summary (continued)
• Constant
– Variable with value that does not change
• Reference variable
– Uses class name as data type
• Operators:
– Mathematic
– Assignment
For in-class practice: p. 113, Ex. 2, 3, 6, 7, 8, 9, 11, 14;
p. 114, PEx. 2, 3, 4, 5; Program: AddTwoNumbers
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