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Visual Basic

Introduction to VB.NET

.NET Framework

VS2008 IDE

How VB is Compiled

Start Visual Studio


Windows Form App


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VB OOP Programming

Visual Basic Code


Exit Code


Button Event Code

Coding Recommendations

If/Then/Else

Error List Window

Comment Syntax

Help Window

Language Essentianl

Built-In Data Types


Declare Variables

Declare Constants

Code Arithmetic Expressions

Assignment Statements

Operator Precedence

Type Casting


Math Class

String Declaration

Conversion Functions

Conversion Methods

Formatting Functions

String Formatting


Variable Scope

Enumerations

Nullable Types


Loop Constructs

For Next Loop

Do While Loop


Do Until Loop

Do...Loop-While

Do...Loop-Until


Exit Do | Exit For

Do...Loop


Nested Loops


Arrays

Array Declaration


Rnd( ) Function

Listbox Control


KeyPressEventArgs


Parallel Arrays

Key Event Args


Dynamic Arrays

Redimension Array

Set Breakpoint

Start Debugger


ReDim Preserve


MultiDimensional Arrays

DataGridView Control


Length and Sort Methods


Structures

Pad Right

Split Method

IsNumeric Function


Multiform Projects


Add Form To Project

Form Object Methods

Form Show Method

ShowDialog Method

Form Close Method

Form Accept Button

Multiform Project Example


ASP.NET Web Programming

Create Data Source


Configure Access Data Source


Add Product Class


Extract Local Database Data

Order PageLoad VB Code

Add New Web Page


Set Start Page

Display Cart Aspx Code

Display Cart Design View

Sorted List Definition

VB.NET Session State


Create CartItem Class

GetCartContents Function


Add To Cart Event Handler

Remove Cart Item Event


Clear Cart Event Handler



How to Declare Variables in Visual Basic

A variable stores a value that can change as the program executes. You must declare a variable before you can use it.

The Syntax to Declare a Variable in Visual Basic

Dim VariableName [As Type] [= Expression]
Visual Basic Variable Declaration Examples
	Dim Counter As Integer
	Dim NumberOfBytes As Long = 20000
	Dim InterestRate as Double = 8.125
	Dim Letter As Char = "A"
	Dim Line1 As String = "This is a string"
						
Summary
  • A variable stores a value that can change as the program executes.
    • You must declare a variable with the Dim statement before you can use it.
  • You may initialize a variable when you declare it. If you do not Visual Basic assigns:
    • A value of 0 to all numeric types.
    • A value of false to Boolean types.
    • An Empty String to String Values.

Figure VB-35: Visual Basic Variable Declaration Syntax and Examples


How to Declare a Constant in Visual Basic

A constant stores data that doesn't change during program execution. Constants must have values assigned to them when they are declared with the Const statement:

Visual Basic Constant Declaration Syntax:

Const Constant Name As type = Expression
Visual Basic Constant Declaration Examples:
	Const DaysInOctober As Integer = 31
	Const StateSalesTax As Double = .07
						
Visual Basic Constant Declaration Summary:
  • A constant stores a value that can't be changed.
  • A literal value refers to a specific numeric value like 2.5 or 1.7

Figure VB-36: Visual Basic Constant Declaration and Syntax


How to Code Arithmetic Expressions

Operator Name Description
+ Addition Adds two operands
- Subtraction Subtracts the right operand from the left operand.
* Multiplication Multiplies the right operand and the left operand.
/ Division Divides the right operand into the left operand.
If both operands are integers, then the result is an integer.
\ Integer Division Divides the right operand into the left operand returning an integer quotient.
Mod Modulus Returns the value that is left over after dividing the right operand into the left operand.
^ Exponentiation Raises the left operand to the power of the right operand.
+ Positive Sign Returns the value of the operand.
- unary negative Changes a positive value to a negative and vice versa.
Visual Basic Arithmetic Operator Summary
  • An arithmetic expression consists of one or more operands and arithmetic operators.
  • The first seven operators in the table above are called binary operators
  • because they work on two operands.
  • The last two operators are called unary operators because they work on one operand.

Figure VB-37: Visual Basic Arithmetic Operators


How to code assignment statements

Operator Name Description
= Assignment Assigns a new value to the variable.
+= Addition Adds the right operand to the value stored in the variable and assigns the result to the variable
-= Subtraction Subtracts the right operand from the value stored in the variable and assigns the result
to the variable.
*= Multiplication Multiplies the variable by the right operand and assigns the result to the variable.
/= Division Divides the variable by the right operand and assigns the result to the variable.
If the variable and the operand are both integers, then the result is an integer.
\= Integer Division Divides the variable by the right operand and assigns the integer quotient to the variable.
Visual Basic Assignment Syntax:

VariableName = Expression
Visual Basic Assignment Statement Examples:
	Counter = 21
	NewCounter = Counter
	Total = Subtotal * DiscountAmount
	Price = Price + .57
	Price += .57
						
Visual Basic Arithmetic Assignment Summary:
  • Assignment Statement: Consists of a variable, an equals sign, and an expression.
  • When the Assignment Statement is executed:
    • The expression is evaluated.
    • The result of the operation stored in the variable.
  • In addition to the equals sign, Visual Basic provides 5 additional assignment operators.
    • These operators provide a shortcut assignment method.

Figure VB-38: Visual Basic Arithmetic Assignment Operators


Visual Basic Arithmetic Operator Order of Precedence

The order in which a statement is evaluated is known as operator precedence. Understanding operator precedence is essential to properly coding and evaluating equations and statements.

Visual Basic Operator Order Of Precedence:
  1. Exponentiation.
  2. Positive and Negative.
  3. Multiplication, Division, Integer Division, Modulus.
  4. Addition and Subtraction.
Visual Basic Operator Order of Precedence Examples:
	Dim DiscountPercent As Double = .2			' 20% Discount
	Dim Price As Double = 100				' Price of $100
	Price = Price * 1 - DiscountPercent			' Price = $99.80

	Dim DiscountPercent As Double = .2			' 20% Discount
	Dim Price As Double = 100				' Price of $100
	Price = Price * (1 - DiscountPercent)			' Price = $80.00
						
Visual Basic Operator Order of Precedence Summary:
  • Operations in an expression are evaluated from left to right in the order of precedence.
  • When Parentheses are used:
    • The operations in the innermost sets of parentheses are done first.
    • Subsequent sets working towards the outermost sets of parentheses are done next.

Figure VB-39: Visual Basic Operator Order of Precedence


How to work with Type Casting in Visual Basic

Implicit Casting Order from less Precise to more Precise Data Types:
Byte → Short → Integer → Long → Decimal → Single → Double
Char → Integer
Implicit Casts for Widening Conversions:
	Dim Grade As Double = 92			' Converts an Integer to Double
	
	Dim A As Double = 6.5
	Dim B As Integer = 6
	Dim C As Integer = 10

	Dim Ave As Double = ( A + B + C ) / 3		' B & C & 3 will be converted to Double
							' Ave = ( 22.5 / 3.0 ) = 7.5
						
Implicit Casts for Narrowing Conversions:
	Dim Grade As Integer = 93.75					' Grade = 94 due to rounding

	Dim Subtotal As Double = txtSubtotal.Text			' May throw exception
	
	Dim Average As Integer = ( A + B + C ) / 3			' Average = 8
						
Explicit Casting with CInt and CDbl Functions:
	Dim Grade As Integer = CInt( 93.75 )				' Grade = 94 due to rounding

	Dim Subtotal As Double = CDbl ( txtSubtotal.Text )		' May throw exception

	Dim Average As Integer = CInt ( CInt ( A ) + B + C ) / 3	' Average = 7
						
Type Casting in Visual Basic Summary:
  • The process of converting one data type to another is called Casting.
  • A Widening Conversion transforms lower precision data to higher precision.
  • Visual Basic does Widening Conversion automatically.
  • A Narrowing Conversion transforms higher precision data to lower precision.
  • In order to avoid exceptions - it is best to perform casting explicitly.

Figure VB-40: Visual Basic Type Casting Examples and Description



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