Control Structures II

October 7, 2015

Control Structures II

• Review
• Nested IF/ELSE
• And/Or Operator
• Short Circuit Evaluation
• Switch
• Not Operator

HW REVIEW

Review

• What can a boolean variable hold?
• What are these: !=, ==, >, <, >=, <=
• What happens in this program when points = 2? points =1? points = 7

Nested If Statements

• We can put if statements inside of if, else or else if statements
• You can do this within if, else, or else if blocks
• Really helps when dealing with complicated logic and ranges

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And Operator

• Used in boolean statements to create a compound expression
• It only allows the boolean statement to be true if BOTH statements are true
• Denoted by two ampersand signs (&&) between two boolean expressions
• boolean seahawksWin = ((russelWilsonYards > 0) && (camChancellorPlays == “yes”));

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Or Operator

• Can be used in a compound boolean expression
• It is used when you want to create a boolean expression that is true when at least one of the boolean clauses is true
• Denoted by two vertical bars (||)
• boolean shouldIPlayWithAnimal = ((animal == “cat”) || (animal == “dog”));

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Short Circuit Evaluation

• Short circuit evaluation occurs when no more computation is needed to determine the answer
• Both && and || use short circuit evaluation
• && : if the first clause is false, we know the whole expression will be false
• || : if the first clause is true, then we know the whole expression must be true

• String animal = “cat”;
• boolean shouldIPlayWithAnimal = ((animal == “cat”) || (animal == “dog”));

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• int russellWilsonYards = 0;
• boolean seahawksWin = ((russelWilsonYards > 0) && (camChancellorPlays == “yes”));

Switch Statement

• We could write a bunch of if statements when testing one variable but there is a cleaner way of doing it
• Switch Statement
• in the parenthesis is the expression you would like to evaluate: “grade”
• each case is a possible value
• break tells the switch statement to terminate
• default is optional and runs when the grade is not found (similar to else)

Not operator

• Negates any boolean expression
• If the boolean expression was true, with the not operator it becomes false
• if the the boolean expression was false, it now becomes true
• The not operator must precede the boolean expression it will negate

Operator precedence

• The book talks about operator precedence on page 283
• I like to view it a simpler way, if you’re not sure of which operator will have precedence, use parentheses and you can explicitly state which one should come first

LAB/HW

No class 10/11 & 10/12