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Published byMarlene Walsh Modified over 3 years ago

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Conditional statements and Boolean expressions

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The if-statement in Java (1) The if-statement is a conditional statement The statement is executed only if a given condition is satisfied An if-statement makes sure that the correct condition is satisfied before a certain action is performed

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The if-statement in Java (2) Syntax of the if-statement: The keyword if announces (to the Java compiler) that we started an if-statement A conditional clause ( CONDITION ) follows the keyword if Following the condition clause, you can write (only) one statement

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The condition clause of the if- statement (1) The condition clause of the if-statement is an expression that evaluates to true or false Expressions that evaluates to true or false are known in Computer Science as: Boolean expressions Example: a < 0

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The condition clause of the if- statement (2)

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Multiple statements in the "then"- part of the if-statement (1) Block = a pair of "{" and "}" braces that groups components in a Java program together

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Multiple statements in the "then"- part of the if-statement (2) Statement block = multiple statements grouped together by braces {.... } A statement block in Java is considered as one (single) statement

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Representation techniques: Flow chart (1) A flow chart is a diagram that represents a computer algorithm. It uses a rectangular box to represent an assignment statement It uses a diamond box to represent a condition Lines are used to indicate the flow of the steps in the algorithm

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Representation techniques: Flow chart (2)

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Representation techniques: Structure diagram(1) A structure diagram is another type of diagram to represent a computer algorithm. It uses different shapes of boxes to represent assignment statements and conditions The structure diagram does not use lines

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Representation techniques: Structure diagram(2)

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The Boolean (logical) data type boolean The boolean data type is a built-in (primitive) data type of Java is used to represent the logical values There are 2 logical values: true and false Encoding scheme used in the boolean data type: 0 represents false 1 represents true uses 1 byte of memory (to store 0 or 1)

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Boolean literals There are 2 boolean literals (= logical constants) in Java: These 2 words are keywords (reserved words) in Java

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Defining boolean typed variables (1) Syntax to define an boolean typed variable: boolean NameOfVariable ; The keyword boolean announces the variable definition clause The NameOfVariable is an identifier which is the name of the variable. The variable definition clause is must be ended with a semi- colon ";“ A boolean typed variable can store true (1) or false (0)

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Defining boolean typed variables (2)

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Operations that return a boolean result 1. Compare operators: A compare operator compares 2 numerical expressions and return a Boolean result. 2. Logical operators: A logical operator compares 2 Boolean (logical) expressions and return a Boolean result

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Compare operators (1) A compare operator will return the value true if the test is successful A compare operator will return the value false if the test is unsuccessful The same automatic conversion rules used for arithmetic operators apply for compare operators

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Compare operators (3) you can assume that all compare operators have the same priority

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Compare operators (4)

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Logical operators (1)

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Logical operators (2)

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Logical operators (3)

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Logical operators (4)

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Programming trick: test if a number is between 2 numbers (1) The program prints "yes" when 10 ≤ a ≤ 20 It is illegal to use the comparison operator "<=" on a Boolean value and a number

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Programming trick: test if a number is between 2 numbers (2)

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Programming trick: test if a number is between 2 numbers (3)

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