Clearly Visual Basic:
Programming with Visual Basic 2010 2nd Edition
Chapter 9
Time to Leave the Nest
(Nested Selection Structures)
Objectives
After studying Chapter 9, you should be able to:
 Nest selection structures
 Include logical operators in a selection structure’s condition
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Nested Selection Structures
 Nested selection structure
 Selection structure contained (nested) within an outer structure
 Figures 9-1 through 9-4
 Shown on following slides
 Show problem specifications and their algorithms
 Problem specification and algorithm are modified
 To use single- and dual-alternative selection structures
 To use nested selection structures
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Nested Selection Structures (cont’d.)
Figure 9-1 A problem that requires a dual-alternative selection structure
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Nested Selection Structures (cont’d.)
Figure 9-2 A problem that requires nested single-alternative selection structures
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Nested Selection Structures (cont’d.)
Figure 9-3 Another problem that requires a dual-alternative selection structure
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Nested Selection Structures (cont’d.)
Figure 9-4 A problem that requires a nested dual-alternative selection structure
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Putting Rob’s Problems Aside
 Figure 9-5
 Shows problem specification and a correct algorithm
 Figure 9-6
 Shows modified problem specification and its algorithm
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Putting Rob’s Problems Aside (cont’d.)
Figure 9-5 Math problem specification and algorithm
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Putting Rob’s Problems Aside (cont’d.)
Figure 9-6 Modified math problem specification and its algorithm
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Let’s Go to the Swap Meet
 Swap the contents of text boxes in Figure 9-9
 Swap is accomplished by:
 Assigning first integer to Number 1 text box
 Assigning second integer to Number 2 text box
 Figure 9-10 on next slide
 Illustrates where to place the swapping instructions
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Let’s Go to the Swap Meet (cont’d.)
Figure 9-10 First modification to the algorithm from Figure 9-6
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
That’s Way Too Logical for Me
 Logical operators (Boolean operators)
 Allow you to combine two or more conditions into one
compound condition
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Figure 9-14
Logical operators and examples
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Figure 9-15 Gross pay problem specification and algorithm
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Figure 9-16 Code corresponding to Figure 9-15’s algorithm
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Summary of Operators
 Figure 9-18 lists operators and their order of precedence
 Arithmetic operators evaluated first
 Comparison operators next
 Then logical operators
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Figure 9-18 Listing of arithmetic, comparison, and logical operators
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Summary
 Both paths in a selection structure:
 Can include nested selection structures
 Nested selection structures
 Used when more than one decision must be made before the
appropriate action can be taken
 When comparing two numbers:
 The first number can be greater than, less than, or equal to the
second number
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition
Summary (cont’d.)
 Logical operators
 Combine conditions into compound condition
 When the AndAlso logical operator is used to combine
conditions:
 All conditions must be True for the compound condition to be
True
 AndAlso operator
 Has a higher precedence than the OrElse operator
 Arithmetic operators
 Evaluated first in an expression
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Clearly Visual Basic: Programming with Visual
Basic 2010, 2nd Edition