mcav_vbdotnet_session3

8/3/2019 MCAV_VBDOTNET_Session3

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VISUAL BASIC.NET


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Methods - Sub Procedures and Functions

A sub procedure is a method that does notreturn any values. In VB.Net, it is defined usingthe Sub keyword. A sub procedure may or maynot accept parameters. For example,

Sub ShowCurrentTime()Console.WriteLine("The current time is: " &

DateTime.Now)

End Sub


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Methods - Sub Procedures and Functions

A function is a type of method that returnsvalues. A function, like a sub-procedure may ormay not accept parameters. For example,

Function FindSum(ByVal num1 As Integer,

ByVal num2 As Integer) As IntegerDim sum As Integer = num1 + num2

Return sum

End Function


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Passing Arguments (ByVal , ByRefkeyword)

Call by Reference makes the changes reflectback in the original variables .

Call By Value works with copies of originalvalues and changes are not reflected back inoriginal values.


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The OptionalKeyword

The parameters of VB.Net methods (subprocedures and functions) can be marked as'Optional'.

The optional parameters must be the final

parameter of a method. A method with an Optional parameter may be

called either with the optional parameter or withoutthe optional parameter.

An Optional parameter is that they must bespecified with the default value.


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Loops and control structures

The If Statement

The Select Case Statement

The Do While and Loop While loops

The For Loop


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If Else

If (Condition)Then

Statements executed if condition is true

Else

Statements executed if condition is false

EndIf

We can also have Else If block in If Elsestatements

Every If statement must contain a then and anend if


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The Select Case statement

Select Case varCase 1

stmt1 // executed if var = 1Case 2

stmt2 // executed if var = 2Case Else

stmt3 // executed if var is other than 1 and 2End Select

The select case statement is a lot like the switchstatement in Java

It can use ANY data type in VB


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Using To and Is in an

ExpressionList To keyword: specifies a range of minimum and

maximum values

Case 1 To 5

Is keyword: specifies a range of values whenyou know only one value, either the minimum orthe maximum

Case Is > 10


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The ForNext Loop

We use the ForNext statement to code a loop

that repeats for a specific number of times


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The ForNext Loop

counteris a numeric variable that keepstrack of how many times the loopinstructions are repeated

startvalue, endvalue, and stepvalue Must be numeric Can be positive or negative, integer or non-

integer

Default stepvalueis 1


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The DoLoop Statement

Unlike the ForNext statement, theDoLoop statement can be used to

code both a pretest loop and aposttest loop


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Do While Loop

Do While(a0)Console.Writeline(a)

a = a 1

Loop

Do

Console.Writeline(a)

a = a 1Loop While(a0)


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Do Until Loop

Do Until(a=0)Console.Writeline(a)

a = a 1

Loop

Do

Console.Writeline(a)

a = a 1Loop Until(a=0)


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Comparison Operators

= Is equal to

> Is Greater Than

>= Is Greater Than or Equal to

< Is Less Than


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Comparison Operators

Comparison operators are also referred to asrelational operators

All expressions containing a relational operatorwill result in either a true or false answer only

Comparison operators are evaluated from left toright, and are evaluated after any mathematicaloperators


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Comparison Operators(continued)

10 + 3 < 5 * 2

5 * 2 is evaluated first,giving 10

10 + 3 is evaluatedsecond, giving 13

13 < 10 is evaluatedlast, giving false

7 > 3 * 4 / 2

3 * 4 is evaluatedfirst, giving 12

12 / 2 is evaluatedsecond, giving 6

7 > 6 is evaluatedlast, giving true


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Logical Operators

Not Reverses the truth value of condition; false becomestrue and true becomes false.

1

And All conditionsconnected by the And operator must betrue for the compound conditionto be true.

2

AndAlso All conditionsconnected by the AndAlso operatormust be true for the compound conditionto be true.

2

Or Only one of the conditionsconnected by the Oroperator needs to be true for the compound conditionto be true.

3

OrElse Only one of the conditionsconnected by the OrElseoperator needs to be true for the compound conditionto be true.

3

Xor One of the conditionsconnected by Xor must be truefor the compound condition to be true.

4


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Short-circuiting evaluations

VB.NET features two logical operators that helpmake programming more logical. These newoperators [AndAlso and OrElse] add a lot to theold And and Or operators.

They offer advantages in two general categories: We can avoid executing part of a logical

expression to avoid problems.

We can optimize code by not executing any

more of a compound expression than required. AndAlso and OrElse are pretty much like And and

Or except that they will "short circuit" anexpression once the outcome is guaranteed.


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Logical Operators

Truth table for And operator

If condition1 is And condition2is

Value of Result is

True True True

True False False

False True False

False False False

Result = condition1 And Condition2


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Logical Operators

Truth table for AndAlso operator


Value of Result is

True True True

True False False

False(not

evaluated)False

Result = condition1 AndAlso Condition2


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Logical Operators

Truth table for Or operator


Value of Result is

True True True

True False True

False True True

False False False

Result = condition1 Or Condition2


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Logical Operators

Truth table for OrElse operator


Value of Result is

True (not evaluated) True

False True True

False False False

Result = condition1 OrElse Condition2


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Logical Operators

Truth table for Xor operator


Value of Result is

True True True

True False False

False True True

False False False

Result = condition1 Xor Condition2


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How to add command line

arguments in Visual Studio IDE ??

mcav_vbdotnet_session3

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