Flowcharting Tutorial

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					Microsoft Visual Basic 2005:
         Reloaded
          Second Edition


           Chapter 4
  Making Decisions in a Program
                                   Objectives

After studying this chapter, you should be able to:
• Include the selection structure in pseudocode and in
  a flowchart
• Write an If…Then…Else statement
• Write code that uses comparison operators and
  logical operators
• Create a variable having block-scope
• Concatenate strings



Microsoft Visual Basic 2005: Reloaded, Second Edition   2
                    Objectives (continued)

•   Use the ControlChars.NewLine constant
•   Change the case of a string
•   Determine whether a string contains data
•   Display a message in a message box
•   Include a nested selection structure in pseudocode,
    a flowchart, and code




Microsoft Visual Basic 2005: Reloaded, Second Edition   3
                    Objectives (continued)

• Code an If/ElseIf/Else selection structure
• Include a Case selection structure in pseudocode, a
  flowchart, and code
• Generate random numbers




Microsoft Visual Basic 2005: Reloaded, Second Edition   4
                   The Selection Structure
• Selection structure (or decision structure):
    – Used to select a path to take based on the outcome of
      a decision or comparison
• Condition:
    – The decision to be made
    – Results in a Boolean (True or False) answer
• Four forms of selection structure:
    –   If
    –   If/Else
    –   If/ElseIf/Else
    –   Case
Microsoft Visual Basic 2005: Reloaded, Second Edition    5
    The Selection Structure (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   6
      Writing Pseudocode for the If and
         If/Else Selection Structures

• If selection structure: contains one set of
  instructions to process when the condition is true
• If/Else selection structure:
    – Contains two sets of instructions
    – One set is processed when the condition is true
    – The other set is processed when the condition is false
• True path: path to follow when condition is true
• False path: path to follow when condition is false



Microsoft Visual Basic 2005: Reloaded, Second Edition      7
      Writing Pseudocode for the If and
         If/Else Selection Structures
                  (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   8
           Flowcharting the If and If/Else
               Selection Structures
• Selection/repetition symbol:
     – Diamond shape
     – Represents both selection and repetition structures
     – One flowline entering and two flowlines leaving




Microsoft Visual Basic 2005: Reloaded, Second Edition        9
         Flowcharting the If and If/Else
        Selection Structures (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   10
      Coding the If and If/Else Selection
                  Structures




Microsoft Visual Basic 2005: Reloaded, Second Edition   11
      Coding the If and If/Else Selection
           Structures (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   12
      Coding the If and If/Else Selection
           Structures (continued)
• Else clause: an optional part of the If statement
• Statement block: set of statements terminated by
  an Else or End If




Microsoft Visual Basic 2005: Reloaded, Second Edition   13
                   Comparison Operators

• Comparison operators (or relational operators):
   – Used as part of the condition in an If statement
• Most commonly used comparison operators:
   –   Equal to: =
   –   Greater than: >
   –   Greater than or equal to: >=
   –   Less than: <
   –   Less than or equal to: <=
   –   Not equal to: <>


Microsoft Visual Basic 2005: Reloaded, Second Edition   14
     Comparison Operators (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   15
     Comparison Operators (continued)
• Comparison operators:
   – Have no order of precedence
   – Are evaluated from left to right in an expression




Microsoft Visual Basic 2005: Reloaded, Second Edition    16
     Comparison Operators (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   17
         Using Comparison Operators –
           Swapping Numeric Values
• Pseudocode for a procedure that displays highest
  and lowest of two numbers:




Microsoft Visual Basic 2005: Reloaded, Second Edition   18
  Using Comparison Operators –
Swapping Numeric Values (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   19
  Using Comparison Operators –
Swapping Numeric Values (continued)
 •Block scope: the scope of a variable created within
 a block
 •Block-scope variable: can only be used within the
 statement block in which it was declared
 •Concatenation operator (&): links two strings
 •ControlChars.NewLine constant:
       –Advances the insertion point to the next line




Microsoft Visual Basic 2005: Reloaded, Second Edition   20
  Using Comparison Operators –
Swapping Numeric Values (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   21
  Using Comparison Operators –
Swapping Numeric Values (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   22
  Using Comparison Operators –
Swapping Numeric Values (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   23
  Using Comparison Operators –
Swapping Numeric Values (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   24
  Using Comparison Operators –
Swapping Numeric Values (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   25
         Using Comparison Operators –
                  Example 2
• Pseudocode for a procedure to allow the user to
  display the sum or difference of two numbers:




Microsoft Visual Basic 2005: Reloaded, Second Edition   26
         Using Comparison Operators –
             Example 2 (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   27
         Using Comparison Operators –
             Example 2 (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   28
         Using Comparison Operators –
             Example 2 (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   29
         Using Comparison Operators –
             Example 2 (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   30
           Using the ToUpper and ToLower
                      Methods
•     String comparisons in Visual Basic are case-sensitive
•     ToUpper method: converts a string to uppercase
•     ToLower method: converts a string to lowercase
•     ToUpper and ToLower can be used to permanently
      or temporarily convert a variable’s contents




    Microsoft Visual Basic 2005: Reloaded, Second Edition   31
       Using the ToUpper and ToLower
            Methods (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   32
       Using the ToUpper and ToLower
            Methods (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   33
       Using the ToUpper and ToLower
            Methods (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   34
                          Logical Operators
• Logical operators (or Boolean operators):
   – Used to combine one or more conditions
• Compound condition: a combination of conditions
  using logical operator(s)




Microsoft Visual Basic 2005: Reloaded, Second Edition   35
           Logical Operators (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   36
         Logical Operators (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   37
            Logical Operators (continued)

• Truth tables: used to evaluate logical operators in an
  expression
• Short-circuit evaluation: an evaluation in which the
  second condition may not be evaluated
• And and Or operations always evaluate both
  conditions
• AndAlso and OrElse operations do not evaluate
  second condition if the first condition is false




 Microsoft Visual Basic 2005: Reloaded, Second Edition   38
           Logical Operators (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   39
           Logical Operators (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   40
                    Using the Truth Tables

• Use And or AndAlso when both conditions must be
  true to give a true result
• Use Or or OrElse when one or both conditions
  must be true to give a true result
• Use XOr when exactly one condition must be true
  to give a true result
• Logical operators are evaluated after arithmetic or
  comparison operators in an expression



Microsoft Visual Basic 2005: Reloaded, Second Edition   41
     Using the Truth Tables (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   42
     Using the Truth Tables (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   43
             Using Logical Operators in an
              If…Then…Else Statement
• Data validation:
   – Verifying that the input data is within the expected range
• Use an If…Then…Else statement to validate input data




 Microsoft Visual Basic 2005: Reloaded, Second Edition      44
     Using Logical Operators in an
 If…Then…Else Statement (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   45
     Using Logical Operators in an
 If…Then…Else Statement (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   46
     Using Logical Operators in an
 If…Then…Else Statement (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   47
       The String.IsNullOrEmpty Method
• String.IsNullOrEmpty method: determine if a
  control’s Text property or String variable contains data




 Microsoft Visual Basic 2005: Reloaded, Second Edition   48
      The String.IsNullOrEmpty Method
                 (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   49
        Modifying the Skate-Away Sales
                   Application




Microsoft Visual Basic 2005: Reloaded, Second Edition   50
        Modifying the Skate-Away Sales
            Application (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   51
        Modifying the Skate-Away Sales
            Application (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   52
        Modifying the Skate-Away Sales
            Application (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   53
        The MessageBox.Show Method

• MessageBox.Show method:
     – Display message box with text, buttons and an icon
• When a message box is displayed, the program
  waits until the user selects a button
• MessageBox.Show returns an integer value
  indicating which button the user selected




Microsoft Visual Basic 2005: Reloaded, Second Edition       54
        The MessageBox.Show Method
                (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   55
        The MessageBox.Show Method
                (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   56
        The MessageBox.Show Method
                (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   57
        The MessageBox.Show Method
                (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   58
        The MessageBox.Show Method
                (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   59
        The MessageBox.Show Method
                (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   60
             Nested Selection Structures

• Nested selection structure: a selection structure
  that is completely contained within another
  selection structure
• Primary decision: decision made by the outer
  selection structure
• Secondary decision: decision made by the inner
  selection structure




Microsoft Visual Basic 2005: Reloaded, Second Edition   61
             Nested Selection Structures
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   62
             Nested Selection Structures
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   63
             Nested Selection Structures
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   64
             Nested Selection Structures
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   65
             Nested Selection Structures
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   66
             Nested Selection Structures
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   67
             Nested Selection Structures
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   68
  The If/ElseIf/Else Selection Structure

• Need a procedure to display a message based on
  a letter grade:

                          Letter grade                  Message
                                  A             Excellent
                                  B             Above Average
                                  C             Average
                                  D             Below Average
                                  F             Below Average

Microsoft Visual Basic 2005: Reloaded, Second Edition             69
  The If/ElseIf/Else Selection Structure
                (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   70
  The If/ElseIf/Else Selection Structure
                (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   71
           The Case Selection Structure
• Case selection structure:
     – Used when there are many paths from which to
       choose
     – Simpler and clearer than using If/ElseIf/Else




Microsoft Visual Basic 2005: Reloaded, Second Edition   72
           The Case Selection Structure
                  (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   73
           The Case Selection Structure
                  (continued)
• Case selection structure in a flowchart:
     – Uses the diamond symbol
     – One flowline into the diamond, but many flowlines
       out of the diamond
• Case selection structure evaluates an expression
  to determine which path to take
• Case selection structure:
     – Begins with Select Case
     – Ends with End Select
     – Has one Case clause for each possible value
Microsoft Visual Basic 2005: Reloaded, Second Edition      74
           The Case Selection Structure
                  (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   75
           The Case Selection Structure
                  (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   76
  Using To and Is in an ExpressionList
• TO and IS keywords: specify a range of values in a
  Case clause’s expression list
• TO:
     – When you know both the upper and lower bounds of
       the range
• IS:
     – When you know only one end of the range
     – Used with a comparison operator



Microsoft Visual Basic 2005: Reloaded, Second Edition   77
  Using To and Is in an Expression List
              (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   78
            Generating Random Integers
• Pseudo-random number generator: produces a
  sequence of numbers that meets certain statistical
  requirements for randomness
• Random.Next method:
     – Generates a random integer
     – Can specify a minimum and maximum value




Microsoft Visual Basic 2005: Reloaded, Second Edition   79
            Generating Random Integers
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   80
            Generating Random Integers
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   81
            Generating Random Integers
                    (continued)




Microsoft Visual Basic 2005: Reloaded, Second Edition   82
                     Programming Tutorial




Microsoft Visual Basic 2005: Reloaded, Second Edition   83
                   Programming Example




Microsoft Visual Basic 2005: Reloaded, Second Edition   84
                                    Summary

• Selection structure is used for decisions
• Four forms of selection structures: If, If/Else,
  If/ElseIf/Else, and Case
• Diamond symbol represents a decision in a
  flowchart
• Expressions with comparison operators will result
  in an answer of True or False
• Variables declared within a selection expression
  have block-level scope


Microsoft Visual Basic 2005: Reloaded, Second Edition   85
                     Summary (continued)

• Concatenation: linking two strings together
• Use logical operators to create compound
  conditions
• String.IsNullOrEmpty method will determine if a
  string contains data
• MessageBox.Show method returns an integer
  indicating which button was chosen
• Selection structures can be nested



Microsoft Visual Basic 2005: Reloaded, Second Edition   86
                     Summary (continued)

• Use If/ElseIf/Else or Case structures when there
  are several possible alternative outcomes
• Use TO keyword to specify a range of valid values
  when both the lower and upper bound are known
• Use IS keyword with a comparison operator to
  specify a lower or upper bound but not both
• Use the pseudo-random number generator to
  generate random numbers



Microsoft Visual Basic 2005: Reloaded, Second Edition   87

				
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