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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №1Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №2Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №3Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №4Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №5Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №6Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №7Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №8Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №9Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №10Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №11Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №12Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №13Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №14Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №15Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №16Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №17Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №18Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №19Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №20Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №21Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №22Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №23Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №24Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №25Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №26Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №27Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №28Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №29Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №30Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №31Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №32Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №33Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №34Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №35Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №36Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №37Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №38Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №39Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №40Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №41Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №42Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №43Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №44
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Programming Logic and Design Seventh Edition Chapter 4 Making Decisions
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Programming Logic and Design Seventh Edition Chapter 4 Making Decisions

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Objectives In this chapter, you will learn about: Boolean expressions and the selection structure The relational comparison operators AND logic OR logic Making selections within ranges Precedence when combining AND and OR operators
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Objectives In this chapter, you will learn about: Boolean expressions and the selection structure The relational comparison operators AND logic OR logic Making selections within ranges Precedence when combining AND and OR operators

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Boolean Expressions and the Selection Structure Boolean expressions can be only true or false Every computer decision yields a true-or-false, yes-or-no, 1-or-0 result Used in every selection structure
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Boolean Expressions and the Selection Structure Boolean expressions can be only true or false Every computer decision yields a true-or-false, yes-or-no, 1-or-0 result Used in every selection structure

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Boolean Expressions and the Selection Structure (continued) Dual-alternative (or binary) selection structure Provides an action for each of two possible outcomes
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Boolean Expressions and the Selection Structure (continued) Dual-alternative (or binary) selection structure Provides an action for each of two possible outcomes

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Boolean Expressions and the Selection Structure (continued) Single-alternative (or unary) selection structure Action is provided for only one outcome if-then
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Boolean Expressions and the Selection Structure (continued) Single-alternative (or unary) selection structure Action is provided for only one outcome if-then

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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №6
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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №7
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Boolean Expressions and the Selection Structure (continued) if-then-else decision if-then clause Holds the action or actions that execute when the tested condition in the decision is true else clause Executes only when the tested condition in the decision is false
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Boolean Expressions and the Selection Structure (continued) if-then-else decision if-then clause Holds the action or actions that execute when the tested condition in the decision is true else clause Executes only when the tested condition in the decision is false

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Using Relational Comparison Operators Relational comparison operators Six types supported by all modern programming languages Two values compared can be either variables or constants Trivial expressions Will always evaluate to the same result Examples: true for 20 = 20? false for 30 = 40?
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Using Relational Comparison Operators Relational comparison operators Six types supported by all modern programming languages Two values compared can be either variables or constants Trivial expressions Will always evaluate to the same result Examples: true for 20 = 20? false for 30 = 40?

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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №10
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Using Relational Comparison Operators (continued) Any decision can be made with only three types of comparisons: =, >, and < The >= and <= operators are not necessary but make code more readable “Not equal” operator Involves thinking in double negatives Best to restrict usage to “if without an else”—that is, only take action when some comparison is false
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Using Relational Comparison Operators (continued) Any decision can be made with only three types of comparisons: =, >, and < The >= and <= operators are not necessary but make code more readable “Not equal” operator Involves thinking in double negatives Best to restrict usage to “if without an else”—that is, only take action when some comparison is false

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Using Relational Comparison Operators (continued)
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Using Relational Comparison Operators (continued)

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Using Relational Comparison Operators (continued)
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Using Relational Comparison Operators (continued)

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Avoiding a Common Error with Relational Operators Common errors Using the wrong operator Think BIG > small Think small < BIG Missing the boundary or limit required for a selection
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Avoiding a Common Error with Relational Operators Common errors Using the wrong operator Think BIG > small Think small < BIG Missing the boundary or limit required for a selection

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Understanding AND Logic Compound condition Asks multiple questions before an outcome is determined AND decision Requires that both of two tests evaluate to true Requires a nested decision (nested if) or a cascading if statement
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Understanding AND Logic Compound condition Asks multiple questions before an outcome is determined AND decision Requires that both of two tests evaluate to true Requires a nested decision (nested if) or a cascading if statement

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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №16
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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №17
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Nesting AND Decisions for Efficiency When nesting decisions Either selection can come first Performance time can be improved by asking questions in the proper order In an AND decision, first ask the question that is less likely to be true Eliminates as many instances of the second decision as possible Speeds up processing time
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Nesting AND Decisions for Efficiency When nesting decisions Either selection can come first Performance time can be improved by asking questions in the proper order In an AND decision, first ask the question that is less likely to be true Eliminates as many instances of the second decision as possible Speeds up processing time

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Using the AND Operator Conditional AND operator Ask two or more questions in a single comparison Each Boolean expression must be true for entire expression to evaluate to true Truth tables Describe the truth of an entire expression based on the truth of its parts Short-circuit evaluation Expression evaluated only as far as necessary to determine truth
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Using the AND Operator Conditional AND operator Ask two or more questions in a single comparison Each Boolean expression must be true for entire expression to evaluate to true Truth tables Describe the truth of an entire expression based on the truth of its parts Short-circuit evaluation Expression evaluated only as far as necessary to determine truth

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Using the AND Operator (continued)
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Using the AND Operator (continued)

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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №21
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Avoiding Common Errors in an AND Selection Second decision must be made entirely within the first decision In most programming languages, logical AND is a binary operator Requires a complete Boolean expression on both sides
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Avoiding Common Errors in an AND Selection Second decision must be made entirely within the first decision In most programming languages, logical AND is a binary operator Requires a complete Boolean expression on both sides

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Understanding OR Logic OR decision Take action when one or the other of two conditions is true Example “Are you free for dinner Friday or Saturday?”
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Understanding OR Logic OR decision Take action when one or the other of two conditions is true Example “Are you free for dinner Friday or Saturday?”

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Writing OR Decisions for Efficiency May ask either question first Both produce the same output but vary widely in number of questions asked If first question is true, no need to ask second In an OR decision, first ask the question that is more likely to be true Eliminate as many extra decisions as possible
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Writing OR Decisions for Efficiency May ask either question first Both produce the same output but vary widely in number of questions asked If first question is true, no need to ask second In an OR decision, first ask the question that is more likely to be true Eliminate as many extra decisions as possible

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Using the OR Operator Conditional OR operator Ask two or more questions in a single comparison Only one Boolean expression in an OR selection must be true to produce a result of true Question placed first will be asked first Consider efficiency Computer can ask only one question at a time
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Using the OR Operator Conditional OR operator Ask two or more questions in a single comparison Only one Boolean expression in an OR selection must be true to produce a result of true Question placed first will be asked first Consider efficiency Computer can ask only one question at a time

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Using the OR Operator (continued)
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Using the OR Operator (continued)

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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №27
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Avoiding Common Errors in an OR Selection Second question must be a self-contained structure with one entry and exit point Request for A and B in English logically means a request for A or B Example “Add $20 to the bill of anyone who makes more than 100 calls and to anyone who has used more than 500 minutes” “Add $20 to the bill of anyone who has made more than 100 calls or has used more than 500 minutes”
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Avoiding Common Errors in an OR Selection Second question must be a self-contained structure with one entry and exit point Request for A and B in English logically means a request for A or B Example “Add $20 to the bill of anyone who makes more than 100 calls and to anyone who has used more than 500 minutes” “Add $20 to the bill of anyone who has made more than 100 calls or has used more than 500 minutes”

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Avoiding Common Errors in an OR Selection (continued)
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Avoiding Common Errors in an OR Selection (continued)

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Avoiding Common Errors in an OR Selection (continued)
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Avoiding Common Errors in an OR Selection (continued)

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Avoiding Common Errors in an OR Selection (continued)
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Avoiding Common Errors in an OR Selection (continued)

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Avoiding Common Errors in an OR Selection (continued)
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Avoiding Common Errors in an OR Selection (continued)

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Avoiding Common Errors in an OR Selection (continued)
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Avoiding Common Errors in an OR Selection (continued)

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Making Selections within Ranges Range check Compare a variable to a series of values between limits Use the lowest or highest value in each range Adjust the question logic when using highest versus lowest values Should end points of the range be included? Yes: use >= or <= No: use < or >
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Making Selections within Ranges Range check Compare a variable to a series of values between limits Use the lowest or highest value in each range Adjust the question logic when using highest versus lowest values Should end points of the range be included? Yes: use >= or <= No: use < or >

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Making Selections within Ranges (continued)
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Making Selections within Ranges (continued)

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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №36
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Avoiding Common Errors When Using Range Checks Avoid a dead or unreachable path Don’t check for values that can never occur Requires some prior knowledge of the data Never ask a question if there is only one possible outcome Avoid asking a question when the logic has already determined the outcome
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Avoiding Common Errors When Using Range Checks Avoid a dead or unreachable path Don’t check for values that can never occur Requires some prior knowledge of the data Never ask a question if there is only one possible outcome Avoid asking a question when the logic has already determined the outcome

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Understanding Precedence When Combining AND and OR Operators Combine multiple AND and OR operators in an expression When multiple conditions must all be true, use multiple ANDs if score1 >= MIN_SCORE AND score2 >= MIN_SCORE AND score 3 >= MIN_SCORE then classGrade = "Pass" else classGrade = "Fail" endif
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Understanding Precedence When Combining AND and OR Operators Combine multiple AND and OR operators in an expression When multiple conditions must all be true, use multiple ANDs if score1 >= MIN_SCORE AND score2 >= MIN_SCORE AND score 3 >= MIN_SCORE then classGrade = "Pass" else classGrade = "Fail" endif

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Understanding Precedence When Combining AND and OR Operators (cont’d) When only one of multiple conditions must be true, use multiple ORs if score1 >= MIN_SCORE OR score2 >= MIN_SCORE OR score3 >= MIN_SCORE then classGrade = "Pass" else classGrade = "Fail" endif
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Understanding Precedence When Combining AND and OR Operators (cont’d) When only one of multiple conditions must be true, use multiple ORs if score1 >= MIN_SCORE OR score2 >= MIN_SCORE OR score3 >= MIN_SCORE then classGrade = "Pass" else classGrade = "Fail" endif

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Understanding Precedence When Combining AND and OR Operators (cont’d) When AND and OR operators are combined in the same statement, AND operators are evaluated first if age <= 12 OR age >= 65 AND rating = "G" Use parentheses to correct logic and force evaluations to occur in the order desired if (age <= 12 OR age >= 65) AND rating = "G"
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Understanding Precedence When Combining AND and OR Operators (cont’d) When AND and OR operators are combined in the same statement, AND operators are evaluated first if age <= 12 OR age >= 65 AND rating = "G" Use parentheses to correct logic and force evaluations to occur in the order desired if (age <= 12 OR age >= 65) AND rating = "G"

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Understanding Precedence When Combining AND and OR Operators (cont’d) Mixing AND and OR operators makes logic more complicated Can avoid mixing AND and OR decisions by nesting if statements
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Understanding Precedence When Combining AND and OR Operators (cont’d) Mixing AND and OR operators makes logic more complicated Can avoid mixing AND and OR decisions by nesting if statements

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Programming Logic and Design Seventh Edition. Chapter 4. Making Decisions, слайд №42
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Summary Decisions involve evaluating Boolean expressions Use relational operators to compare values An AND decision requires that both conditions be true to produce a true result In an AND decision, first ask the question that is less likely to be true An OR decision requires that either of the conditions be true to produce a true result
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Summary Decisions involve evaluating Boolean expressions Use relational operators to compare values An AND decision requires that both conditions be true to produce a true result In an AND decision, first ask the question that is less likely to be true An OR decision requires that either of the conditions be true to produce a true result

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Summary (continued) In an OR decision, first ask the question that is more likely to be true For a range check: Make comparisons with the highest or lowest values in each range Eliminate unnecessary or previously answered questions The AND operator takes precedence over the OR operator
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Summary (continued) In an OR decision, first ask the question that is more likely to be true For a range check: Make comparisons with the highest or lowest values in each range Eliminate unnecessary or previously answered questions The AND operator takes precedence over the OR operator

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