Visual Programming 3

8/7/2019 Visual Programming 3

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Visual ProgrammingVisual ProgrammingStatements in Visual Basic



Boolean Variables and Expressions

Input boxInput box

What Are Conditional Statements?Using AND and OR in Boolean ExpressionsUsing AND and OR in Boolean Expressions

Using the NOT operator Using the NOT operator

Objectives



Boolean Variables

Boolean variable stores one of the following

constant values: "True", or "False"."True", or "False".

For example:Dim Kuku As BooleanDim Kuku As Boolean

Kuku = TrueKuku = True

Dim YoYo As BooleanDim YoYo As Boolean

YoYo = FalseYoYo = False

What are the True and False stand for?

They are the result of every "Boolean expression´"Boolean expression´



Examples - Boolean Expressions

Boolean expression is like a question that the answer to it is "True" True"

or "False"or "False"For example:

�Is 4 Plus 6 is 10? TrueTrue

�Is 2 bigger than 4? FalseFalseBut the question

How much is 4 Plus 6?

�Is not a boolean expression, because its answer

�is 10 (and not True or False)Examples of Boolean expressions in the next slide




The following code:

Dim ABC As BooleanDim ABC As BooleanABC = (3 > 4)ABC = (3 > 4)

Print ABCPrint ABC

Will print "False" on the form.Will print "False" on the form.

The value of the Boolean expression 3 > 4The value of the Boolean expression 3 > 4isis "False","False", becausebecause 3 is not greater than 43 is not greater than 4.



� The following code:

Dim ABC As Boolean

ABC = ("abf" = "abf")Print ABC


Will print "True" on the form.The value of the boolean expression "abf " = "abf³ is "True", because"abf " = "abf³ is "True", because

"abf " is equal to "abf ""abf " is equal to "abf "



� The following code:

Dim ABC As BooleanDim ABC As Boolean

Dim A As Integer Dim A As Integer

Dim B As Integer Dim B As Integer

A = 1A = 1

B = 2B = 2

ABC = (A + 1 = B)ABC = (A + 1 = B)

Print ABCPrint ABC


Will print "True" on the form,

because the value of the Boolean expression

(A + 1 = B) is "True".

In Boolean expressions you can use the

following signs:

= Equal to<> Not Equal to

> Greater than

< Smaller than

>= Greater than or Equal to

<= Smaller than or Equal to



INPUT BOX

� InputBox

� In the next examples we want to receive a value from the user when theprogram is running.

� To do so we will use the InputBoxInputBox command.The InputBox command syntax is:

VariableName = InputBox ("Text to Display")

� After executing this command, the variable will get the value that the user hasentered.

� Example:

�Put 1 Command button on your form and

� enter the following code to its click event:

Dim Elvis As String

Elvis = InputBox("Please Enter your name")

Print Elvis

� Run the program and click the button. A Message Box is appearing with the

� text "Please Enter your name³ as in Figure 1



Conditional Statements

� The syntax of the conditional statement:

If (boolean expression) ThenThe code to execute if the boolean expression is equal to True

ElseThe code to execute if the boolean expression is equal to False

End If

� Lets make a password protected program. We want to promptthe user to enter the password at the very start of the program,so put the following code in the Form_ Load event:

Dim Password As String

Password = InputBox("Please enter the password")If (Password = "let me in") ThenIf (Password = "let me in") Then

MsgBox "The Password is correct!"MsgBox "The Password is correct!"

ElseElse

MsgBox "Incorrect Password!"MsgBox "Incorrect Password!"

End If End If



Using "And" and "Or " In Boolean

Expressions

� How can we make a boolean expression that will be "True"

if the Password is "let me in" or "sam sent me³ ?

Put the following code in your Form_Load event:Put the following code in your Form_Load event:

Dim Password As StringDim Password As String

Password = InputBox("Please enter the password")Password = InputBox("Please enter the password")

If (Password = "let me in") Or (Password = "sam sentIf (Password = "let me in") Or (Password = "sam sent

me") Thenme") Then

MsgBox"The Password is correct!

"MsgBox

"The Password is correct!

"

ElseElse

MsgBox "Incorrect Password!"MsgBox "Incorrect Password!"

EndEnd

End If End If

Run the program.

Lets see what effect has the "Or " operator on the boolean expression we used:Lets see what effect has the "Or " operator on the boolean expression we used:(Password = "let me in") Or (Password = "sam sent me")(Password = "let me in") Or (Password = "sam sent me")

First, the left and right boolean expressionsFirst, the left and right boolean expressionsare being evaluatedare being evaluated

For example, For example, if the Password is "let me in"if the Password is "let me in" thenthen(Password = "let me in") is True(Password = "let me in") is True

andand (Password = "sam sent me") is False(Password = "sam sent me") is False..

Then the boolean expression is look like this:Then the boolean expression is look like this:

(True) Or (False)(True) Or (False)True Or False = TrueTrue Or False = True

So the final result of the expression is True .So the final result of the expression is True .



Using "And" and "Or " In Boolean Expressions

� The "And" operator is similar to the "Or³ operator , except it hasdifferent Effects on boolean expressions:

True And True = TrueTrue And False = False

False And True = False

False And False = FalseFor example, copy the following code to your Form_Load event:

Dim UserName As String

Dim Password As StringUserName = InputBox("Please enter the user name")

Password = InputBox("Please enter the password")

If (Password = "let me in") And (UserName = "elvis") Then

MsgBox "The login is correct!"

Else

MsgBox "Incorrect Login!"

EndEnd If

This code will pop up two InputBoxes.

The first will ask you to enter the user name, and the second will ask

you to enter the password.

The login will be correct only if both user name and password are

correct. The boolean expression (Password = "let me in") And

(UserName = "elvis") is True only if (Password = "let me in") is True,

and (UserName = "elvis") is True, because True And True = True, and

any other combination is equal to False.



Using The "Not" Operator

� Lets see an example of using the operator "Not".

� Copy the following code to your Form_ Load event:

Dim Password As String

Password = InputBox("Please enter the password")

If Not (Password = "let me in") Then

MsgBox "Incorrect Password!"

End

End If

The boolean expression: Not (Password = "let me in") is True only if thePassword is not "let me in". Why?

If the Password is not "let me in",(Password = "let me in") is False ,

and we get the boolean expression: Not (False).Not False = True, so eventually,

the expression value is True

Visual Programming 3

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