Decision Structures

1
Decision Structures
2
Spacecraft

• Divine Vessel V will orbits earth 14 times in 21
  hours
• First manned spacecraft of China, only the third
  country that can send

3
Decisions (If Statements)

• Comparison Operators (gt, lt , ltgt, )
• Logical Operators (and, or, not)
• TRUE or FALSE determines whether to proceed!

4
Questions
If Temp lt 32 Then
True
False
It is warm!
It is COLD!
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If Statements

• If weather PRECIPITATION Then
• It is raining or snowing
• If TEMP lt 32 Then
• It is COLD!
• If temp lt 32 Then
• picture1.print It is FREEZING!
• End If

6
Comparison Operators

• See table 5.1
• equal to
• ltgt unequal to
• lt less than
• gt greater than
• lt less than or equal to
• gt greater than or equal to
• Works both for numbers and strings.

7
Logical Operators

• And, Or, Not
• a gtb And b ltgt 2
• a gtb Or b ltgt 2
• And statements Both must be true
• Or statements one or both must be true
• Not statements True if statement is false

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Boolean value

• Comparison operator and logical operator will
  return a Boolean value.
• Boolean value has only two possibilities True
  and False

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Test for Snowing

• What are conditions for snowing?
• Temperature?
• Precipitation?

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Ands and Ors

• If (weather PRECIPITATION) And (TEMP lt 32)
  Then
• Tests for snow
• If (weather PRECIPITATION) Or (TEMP lt 32)
  Then
• Tests for bad weather

And
Or
NO
NO
PRECIP
PRECIP
lt32
lt 32
T
F
T
T
F
F
gt32
gt 32
F
T
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If Blocks (True and False Options)

• If condition1 Then
• Statements
• Else
• Statements
• End If

12
If-then-else Blocks

• If temp lt 32 Then
• picture1.print It is FREEZING!
• Else
• picture1.print It is not freezing
• End If

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Nested if-then-else structure

• If weather PRECIPITATION then
• If TEMP lt32 then
• Picture1.Print Snowing
• Else
• Picture1.Print raining
• End if
• Else
• If TEMP lt32 then
• Picture1.Print cold day
• Else
• Picture1.Print warm day
• End if
• End if

14
If ElseIf Else Blocks

• Get answer to question, Did you
• have a fun spring break?
• answer Ucase(text1.text)
• answer Trim(answer)
• If answerYES Then
• picture1.print Cool.
• ElseIf answerNO Then
• picture1.print Sorry.
• Else
• picture1.print Cant you even answer the
  question?
• End If

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What if you have a bunch of choices?

• Case Selectors are great for multiple choices
• Best for equalities, not inequalities

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Select Case Blocks

• Allows multiple options (not just true or false)
• Select Case Variable
• Case Condition1
• Case Condition2
• Case Condition3
• Case Else
• End Select

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Name Case

• Select Case Name
• Case George W. Bush
• picture1.print Bring them on.
• Case terminator T-100
• picture1.print Alta vista babe.
• Case Conan O'Brien
• picture1.print This is such a good show.
  What a nice show... Great show
• Case Else
• picture1.print Wow, who is this guy!
• End Select

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Quadratic equation

• aX2bXc0
• What is the solution to X?

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Solution
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Quadratic Formula Solver
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Quadratic Equation

• Write an algorithm for using the quadratic
  formula to determine if there are real roots for
  the equation
• Will the program crash if b2-4ac lt 0?
• If you take square root for a negative number you
  will get a run time error.
• The program should be able to deal with both real
  and complex solutions.