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Selection LogicBuilding decision-making into programs
Sample Problem (v1)• Create an application to allow a store clerk to enter:
• the price of a dozen roses• the number of dozens desired
• Calculate and display the total cost of the order
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Sample Problem (v1)
Figure 4-2: Rosebud Roses application (sequence structure only)
Sample Problem (v1)
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Sample Problem (v1)• Download and look at code
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Sample Problem modified (v2)• Create an application to allow a store clerk to enter:
• the price of a dozen roses• the number of dozens desired
• Customers who order more than 2 dozen roses get a 10% discount
• Calculate and display the total cost of the order
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Modified Problem (v2)
Figure 4-3: Modified Rosebud Roses application (single-alternative selection structure)
Figure 4-4: Single-alternative selection structure shown in a flowchart
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Coding Single-Alternative and Dual-Alternative Selection Structures
• The If…Then…Else statement is used for coding single-alternative and dual-alternative selection structures
• The set of statements contained in each path is referred to as a statement block
Figure 4-6: How to use the If…Then…Else statement (continues)
Modified Problem (v2)• Modify our code as seen in previous slide
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Sample Problem modified (v3)• Create an application to allow a store clerk to enter:
• the price of a dozen roses• the number of dozens desired
• All customers get a discount• Customers who order more than 2 dozen roses get a 10%
discount• All other orders get a 5% discount
• Calculate and display the total cost of the order
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Sample Problem Modified (v3)
Figure 4-5: Modified Rosebud Roses application (dual-alternative selection structure)
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Coding Single-Alternative and Dual-Alternative Selection Structures (cont’d.)
Figure 4-6: How to use the If…Then…Else statement (continues)
Modified Problem (v3)• Modify our code as seen in previous slide
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Comparison (Relational) Operators• Each comparison operator (also referred to as relational
operators) can be used to compare two values, and the comparison always results in a Boolean value: either True or False. • When comparing values, keep in mind that equal to (=) is the opposite
of not equal to (<>), greater than (>) is the opposite of less than or equal to (<=), and less than (<) is the opposite of greater than or equal to (>=)
Figure 4-7 How to use comparison operators in a condition (continues)
( in math ≥ )
( in math ≤ )( in math ≠ )
Modified Problem (v4)• Instead of 2 discount rate levels, have 3 discount rate levels:
• 1 or 2 dozen: 5%• 3 to 6 dozen: 10%• More than 6 dozen: 20%
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Modified Problem (v4) flowchart a
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Order <= 2
Order <= 6
discountRate = .10discountRate = .20
discountRate = .05
T
T
F
F
Modified Problem (v4) flowchart b
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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Order > 6
Order > 2
discountRate = .10discountRate = .05
discountRate = .20
T
T
F
F
Modified Problem (v4) code b
Microsoft Visual Basic 2012: Reloaded, Fifth Edition
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If ordered > 6 Then discountRate = 0.2Else If ordered > 2 Then discountRate = 0.1 Else discountRate = 0.05 End IfEnd If
If ordered > 6 Then discountRate = 0.2Elseif ordered > 2 Then discountRate = 0.1Else discountRate = 0.05End If