selection logic building decision-making into programs

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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Sample Problem (v1)

Figure 4-2: Rosebud Roses application (sequence structure only)

Sample Problem (v1)


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Sample Problem (v1)• Download and look at code


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Sample Problem modified (v2)• Create an application to allow a store clerk to enter:


• Customers who order more than 2 dozen roses get a 10% discount



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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


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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


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Sample Problem modified (v3)• Create an application to allow a store clerk to enter:


• All customers get a discount• Customers who order more than 2 dozen roses get a 10%

discount• All other orders get a 5% discount



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Sample Problem Modified (v3)

Figure 4-5: Modified Rosebud Roses application (dual-alternative selection structure)


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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


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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%


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Modified Problem (v4) flowchart a


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Order <= 2

Order <= 6

discountRate = .10discountRate = .20

discountRate = .05

T

T

F

F

Modified Problem (v4) flowchart b


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Order > 6

Order > 2

discountRate = .10discountRate = .05

discountRate = .20

T

T

F

F

Modified Problem (v4) code b


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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

selection logic building decision-making into programs

Documents

ordermicrosoft visual

codemicrosoft visual

edition2microsoft visual

total cost

store clerk

statement block figure

end ifend ifif

boolean value