basically you can write this expression using a combination of if and else statements, but using the...

8/9/2019 Basically You Can Write This Expression Using a Combination of if and Else Statements, But Using the IFF Results i

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visual Basic .NET language Quick Overview

Despite its ease of use, VB.NET is cable of doing all the things you want like component-based

programming using object oriented programming (OOP). You can define new types, you can create new

classes and their respective properties and methods. Your classes can incorporate OOP features like

inheritance, polymorphism and encapsulation.

So in summary, VB.NET can: define new types (classes), class properties and methods, inheritance,

polymorphism, encapsulation, interfaces, structures, events, attributes etc.

Hello Word!

Console Application

Module YourFirstVBProgram

Sub Main()

System.Consoloe.WriteLine(Hello, World!)

End Sub

END Module

ASP.NET Page

Response.Write(Hello, World!)

Fundamentals

Types


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There are built in types like Boolean and Integer, and there are custom types that you can create

yourself like classes.

For numerical values, you can use the following types: Integer, Short or Long. If you require more

precision use: Single, Double or Decimal. For a single character use: Char.

Many times you want to assign the value of one type to another type, this is commonly referred to as

Casting.

An example would be assigning a variable of type Integer to another variable of type Double. Since all

values of an integer can be held by a Double type, there is no conversion necessary. This is sometimes

referred to as a widening conversion as oppose to a narrowing conversion like when you assign a

Integer value to a Short type. The difference between the two is that a widening conversion is done

automatically i.e. you dont have to do anything special whilst coding. On the other hand, a narrowing

conversion will require you to cast the value (Note: if you have Option Explicit set to off you will not

have to do this, a potential for danger!).

Explicit Cast Example

Dim dlbNumberOfDaysInAYear As Double = 183.5

Dim iMyAge = CType(dlbNumberOfDaysInAYear, Integer) explicit cast

Explicit Casting Methods include: CBool(), CByte(), CChar(), CDate(), CDbl(), CDec(), Dint(), CLng(), CObj(),

CShort(), CStr(), CStr(), CType()

Identifiers

An identifier is simply the name you choose for your variables, objects etc. In VB.NET, your identifier

must begin with either a letter or underscore ('_'). If your coming from a C# background, keep in mind

that identifiers are NOT case sensitive, so both strUserName and strusername are the same thing!

Variables and Constants


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A variable is declared by first typing the type, following by the name you want to call the variable.

Variables will be defaulted to a defaulted value if you fail to initialize the variable.

# All numeric types will be assigned to 0.

# Date type will be given the value of 12:00:00AM 1/1/1001

# Boolean type is False.

# Char type is defaulted to ''.

# String values are "".

The following is an example of declaring an Integer type variable and initializing it to the value of 7,

following by assigning it a new value of 15.

Dim iUserAge As Integer = 7

Integer = 15

To make a variable a constant (a variable whos value cannot change) you simply do:

Const iUserAge As Integer = 7

Enumerations

An enumeration allows you to group a list of named constants, whos type can be either Integer (default

type), Short or Long.

Public Enum CarManufacturers


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Honda = 1

Ford = 2

Toyota = 3

Ferrari = 5

Nissan = 6

End Enum

The default number that an enumeration starts off is 0 unless you explicity assign a different value like I

did above.

To output the value of an enumeration you must cast to the type you chose, example:

Response.Write(String.Format("Honda has been assigned the number {0}", _

CType(CarManufacturers.Honda, Integer))


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Conditional Branching

Branching statements give you control of how your program will flow.

IF & Else Statements

If expression Then

statements

End If

If expression Then

statements

Else

statements

End If

So lets say you want to compare two peoples year of birth:

Dim johnsYear As Integer = 1960

Dim bobsYear As Integer = 1974

If johnsYear > bobsYear Then

Response.Write("John is older!")

Else

Response.Write("Bob is older!")

End If


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ElseIf

The keyword ElseIf allows you to perform many If statements, so if the first If statement evaluates to

false, then it will continue on to the next ElseIf. Once you reach the first ElseIf that evaluates to True no

other ElseIf statement will be evaluated.

If johnsYear > bobsYear Then

statements

ElseIf johnsYear > 1950 Then

Statements

..

..

End If

IFF is yet another conditional branching option which reads "If and only If". There are 3 key parts to

using IFF, they are:

# The Boolean expression that you are testing.

# The value that is going to be returned if the Boolean expression returns a value of True.

# The value that is going to be returned if the Boolean expression returns a value of False.

Basically you can write this expression using a combination of If and Else statements, but using the IFF

results in only 1 line of code.

Say you want to assign a integer variable a value of 10 if John is older, or 5 if he is younger than Bob, the

code would look like:

Dim someVariable As Integer


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someVariable = CInt(IFF(johnsYear > bobsYear), 10, 5))

Select Case Statement

Usually if you have many IF/ELSE/END If combinations, you can clean up your code and use a more

elegant looking Select Case statement. Basically you are forcing your program to find a match and

execute the resulting code.

Select johnsYear

Case 1920

Response.Write("You old man!")

Case 1950

Response.Write("Mid life crisis are we?")

Case 1970

Response.Write("Just say no to drugs!")

Case 1990

Response.Write("Change my diaper!")

End Select

To make things even cleaner, you could create an Enumeration for the years and use that in your Select

statement.

Looping in VB

VB.NET ships with many interation type statements, including: For Each, For, Do and the GoTo.

For Each Looping Statement

With the for each looping statement you can loop through various items in a collection.


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Example: (You have an array of strings)

Dim strCars As String() = {"Honda", "Toyota", "Ford"}

Dim strCar As String

For Each strCar in strCars

Response.Write("

Car: " & strCar")

Next strCar

For Loop

This is a very popular form of looping, one that you will see used very often whilst coding.


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Example:

Dim myCounter As Integer = 0

For myCounter To 100

Response.Write("Still Looping!")

Next

Do Looping

The Do loop is basically a loop that continues until a condition becauses True/ False.

There are different variants of this type of loop, such as Do While, Do & Loop Until, Do Until, Do & Loop

While.

Example of a Do While loop:

Dim iMaximumAge As Integer = 35

Dim iMyAge As Integer = 28

Do While iMaximumAge > iMyAge

iMyAge = iMyAge + 1

Loop

The other forms of Do looping is:

Do Until


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Loop

Do

Loop While

Do

Loop

Do

Loop Until

While

End While

GoTo Statement

This statement should be used with caution as it often results in very confusing code. The GoTo

statement consists of 2 basic elements:


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1) The Label - this consists of the name of the label followed by a colon

2) The 'GoTo' statement that references the label in 1).

Example:

Dim iLoopCount As Integer = 0

Some_label: ' this is the label

iLoopCount = iLoopCount + 1

If iLoopCount < 5 Then

GoTo Some_label

End If


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Operators

Operators in Visual Basic .NET include: +, =, >,


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Comparison Operator '>, =,


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Dim xyz As String = " VB.NET programming"

Dim def As String = abc & xyz ' or you could have used the + operator

Relational Operators: =, etc.

These operators will compare to values and then return either a True or a False (Boolean).

The '' operator stands for Not Equal, so:

Dim a1 As Integer = 10

Dim a2 As Integer = 20

If a1 a2 Then

Response.Write("Not equal is True!")

End If

Exponential Operator '^'

This operator allows you to raise a number to the power of the exponent. So 2^5 will return 25.

Modulus Operator (Mod)

This operator returns the remainder after a division has taken place. An example would be 10 Mode 3

which will return 1.

Logical Operators


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A logical operator allows you to test whether a statements conditions are True or False, or if both

conditions are True or if both conditions are False.

# And - both conditions must result to True

# Or - One of the 2 conditions must result to True

# XOr - results to True ONLY if 1 of the 2 conditions is true

# Not - results to True if the conditions result to False.

If you are confused, maybe you should read up on logical operators:

http://homepages.inf.ed.ac.uk/rbf/HIPR2/logic.htm

Strings

A String type is declared as follows:

Dim myString as String:

A string is initialized as follows:

Dim myString as String = "Hello, World!"

OR

myString = "Hello, World!" ' assuming it was already declared earlier

Strings are Immutable, meaning once you assign a value to them they cannot be changed. Whenever

you assign another value to a string or concatenate a value to a string, you are actually creating a new

copy of a string variable and deleting the old copy of the string. (This has potential performance

considerations if you are doing repeated work on a string variable, use the StringBuilder for such tasks as

it is not immutable ie. The StringBuilder is Muttable).


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There are many useful methods avaible to you when playing with strings, some of the are: Trim(),

ToUpper(), ToLower(), SubString(), StartsWith(), Compare(), Copy(), Split(), Remove() and Length.

Arrays

OOP, Classes & Objects

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