CS3 if statement Visual Basic

Question 1

The Decision Structure allows the code to do different actions based on conditions; in other words it makes decisions.

Question 2

The If…Then Statement

Answer 2

The If…Then Statement Causes Other Statements to Execute Only Under a Certain Condition

Question 3

condition’s syntax relational operators

Answer 3

n Usually a condition is formed using a relational operator n A relational operator determines if a specific relationship exists between two values n > Greater than n < Less than n = Equal to (you’ll learn how to distinguish between = relational operator and = assignment statement from the ‘context) n <> n >= n <= Not equal to Greater than or equal to Less than or equal to

Question 4

binary operatros

Answer 4

Relational operators use two operands, e.g. length>width Islengthgreaterthanwidth? size <= 10 Is size less than or equal 10? n Relational operators yield a True or False result, or a Boolean value

Question 5

operands

Answer 5

operand ‘3’ is one of the inputs (quantities) followed by the addition operator, and the operand ‘6’ is the other input necessary for the operation.

Question 6

Thus far, our code has been executed sequentially in a sequence structure

n To write meaningful programs we need multiple paths of execution

n Somestatementsshouldbeexecutedundercertain circumstances in a decision structure

n Thisunitpresentsthemeanstoexecute statements conditionally

Question 7

THE AND OPERATOR CHART

THRUTH TABLE

Answer 7

Question 8

THE Or OPERATOR

THRUTH TABLE

Answer 8

Question 9

NOTE ITS WRONG TO SAY

Answer 9

n Ifgrade>0And<60 Then
n Theabovewillcauseasyntaxerror ngrade>0isavalidcondition
n But<60isnotavalidcondition

n Recalleachconditionrequirestwooperandsand one relational operator.

Question 10

PRECEDENCE OF LOGICAL OPERATORS

Answer 10

n Logical operators have an order of precedence just as arithmetic operators do

n From highest to lowest precedence n Not

n And n Or n Xor

n As with arithmetic operations, parentheses are often used to clarify order of operations

Question 13

the decision structure

Answer 13

Flowchart of a typical decision structure

n Evaluate the condition

Is it cold outside?

Is it cold outside?

False

True

If yes (True), wear a coat, if not (False), in this example, do nothing.

Question 14

if then statements syntax

Answer 14

If condition Then statement

(more statements as needed)

End If

n New keywords used above: n If

n Then n End

Question 15

conditina of reals sytaz’s relational operators

Answer 15

Usually a condition is formed using a relational operator
n A relational operator determines if a specific relationship exists

between two values n > Greater than
n < Less than

n = Equal to
(you’ll learn how to distinguish between = relational operator and = assignment statement from the ‘context)

n <> n >= n <=

Not equal to
Greater than or equal to Less than or equal to

Question 16

binary operators

Answer 16

Relational operators use two operands, e.g.length>width Islengthgreaterthanwidth?

size <= 10 Is size less than or equal 10?

n Relational operators yield a True or False result, or a Boolean value

Question 17

operators

Answer 17

An operator in a programming language is a symbol that tells the compiler or interpreter to perform specific mathematical, relational or logical operation and produce final result.

Question 18

IF…THEN RULES

Answer 18

he If and the Then keywords must be on the same line

n Only a comment may follow Then on the same line n The End If must be on a separate line
n Only a comment may follow the End If

Recall a Keyword is a reserved word that has a special meaning to the compiler. Do not use keywords as variable or control names as this may result in a syntax error

Question 19

IF THEN CONVENTIONS

Answer 19

The code between the If…Then and the End If is indented

n Visual Basic does not require this
n It is a convention among programmers to aid in the

readability of programs

n By default, the Visual Basic editor will automatically do this indentation as you type your code

Question 20

RELATIONAL OPERATORS WITH MATH OPERATORS

Answer 20

Either or both relational operator operands may be expressions

n Math operators are evaluated before relational

operators

n x+yanda-bareevaluatedfirst
n Each result is then compared using

Question 21

Either or both relational operator operands may be function calls

Question 22

BOOLEAN VARIABLES AS FLAGS

Answer 22

A flag is a Boolean variable that signals when some condition exists in the program

n Since a Boolean variable is either True or False, it can be used as the condition of an If

n Notethatanoperatorisnotrequired

Question 23

= HAS TWO MEANINGS

Answer 23

Relational Operator: If x = y Then

‘….some code End If

n Assignment Statement: Quantity = Textbox1.Text

Question 24

THE IF… THEN…ELSE STATEMENT

Answer 24

The If…Then…Else Statement Executes One Group of Statements If the Condition Is True and Another Group of Statements If the Condition Is False

Question 25

The If…Then construct will execute or ignore a group of statements

(do something or do nothing)

Question 26

The If…Then…Else construct will execute one group of statements or another group (do this or do that)

Question 27

If temperature < 40 Then
lblMesage.Text = “A little cold, isn’t it?”

Else
lblMesage.Text = “Nice weather we’re having!”

End If

IF THEN… ELSE EXAMPLE

Question 28

THE IF … THEN ELSE… ELSE IF

Answer 28

The If…Then…Elseif Statement Is Like a Chain of If…Then…Else Statements

They Perform Their Tests, One After the Other, Until One of Them Is Found to Be True

Question 29

TWO MUTUALLY EXCLUSIVE CHOICES

Answer 29

The If…Then…Else has two choices
n The condition will be True or False
n So one of the two choices must be selected
n They are mutually exclusive (only one can be true)

Question 30

MULTIPLE MUTUALLY EXCLUSIVE CHOICES

Wear a coat

Elseif it is chilly Wear light jacket

Elseif it is windy Wear a windbreaker

Elseif it is hot Wear no jacket

Answer 30

The If…Then…ElseIf statement allows for an entire series of mutually exclusive choices

n In pseudo code (not VB yet):

Question 31

Each of the series of conditions in an If…Then… ElseIf is tested in sequence

Question 32

When a condition is true, the remaining conditions are ignored

Question 33

The order of the conditions is vital
n Wrongordercanresultinwrongdecision

n Whatifit’schillyandwindy?

n Ifwindyistestedbeforechilly,you’dgooutwitha windbreaker when you need a jacket

Question 34

IN VISUAL BASIC SNYTAX

If condition1

Then Statement(s)1

Elseif condition2

Then Statements(s)2

Elseif condition3

Then Statements3

…

End If

Question 35

EXAMPLE OF ElseIf USAGE

Question 36

Question 37

THE (OPTIONAL) TRAILLING ElseIf

Answer 37

n A sequence of ElseIf’s may end with a plain Else, called a trailing Else

n If none of the conditions are True, the trailing Else statement(s) will be executed

n Remember, you code based on the logic (the flowchart).

Question 38

NESTED IF STATEMENTS-

OPTIIONAL TOPICS

Answer 38

A Nested If Statement Is an If Statement in the Conditionally Executed Code of Another If Statement

Focus on the previous slides then move to Nested If Statements

Question 39

Any type of statement may be used inside thestatement(s) portion of any form of If

n This includes other If statements

n If statements within If statements create a more complex decision structure called a Nested If

Answer 39

IF STATEMENTS WITHIN IF STATEMENTS

Question 40

NESTED IF STATEMENTS

Answer 40

If sngSalary > 30000 Then If intYearsOnJob > 2 Then

lblMessage.Text = “The applicant qualifies.” Else

lblMessage.Text = “The applicant does not qualify.” End If

Else If intYearsOnJob > 5 Then

lblMessage.Text = “The applicant qualifies.” Else

lblMessage.Text = “The applicant does not qualify.” End If

End If

Note how the convention of indentations

Question 41

LOGICAL OPERATORS

Answer 41

Logical Operators Connect Two or More Relational Expressions Into One, or Reverse the Logic of an Expression

Question 42

VISUAL BASIC LOGICAL OPERATORS

Answer 42

Not

Reverses the logical value of an expression

Question 43

VISUAL BASIC LOGICAL OPERATORS

Answer 43

Xor

One operand (but not both) must be true for the overall expression to be true, otherwise it is false

Question 44

VISUAL BASIC LOGICAL OPERATORS

Answer 44

Xor

One operand (but not both) must be true for the overall expression to be true, otherwise it is false

Question 45

VISUAL BASIC LOGICAL OPERATORS

Answer 45

Or

One or both operands must be true for the overall expression to be true, otherwise it is false

Question 46

VISUAL BASIC LOGICAL OPERATORS

Answer 46

Operator Effect
And Both operands must be true for the overall

expression to be true, otherwise it is false