07a-Expressions-remainder

07a-Expressions-rema - || “or” p || q true if p or q(or both are true boolean p =(x!= 1 ||(x!= 2 p is always true you really want boolean p

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Boolean Expressions • Boolean expression is just a test for a condition • Essentially, evaluates to true or false • Value comparisons: == “equals” (note: not single = ) != “not equals” (cannot say <> ) > “greater than” < “less than” >= “greater than or equal to” <= “less than or equal to”
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More Boolean Expressions • Boolean comparisons (in order of precedence): ! “not” !p if p is true, then !p is false, and vice versa “and” nly true if d e both true only true if p and q are both true
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Unformatted text preview: || “or” p || q true if p or q (or both) are true boolean p = (x != 1) || (x != 2); p is always true , you really want: boolean p = (x != 1) && (x != 2); Short Circuit Evaluation • Stop evaluating boolean expression as soon as we know the answer • Consider: p = (5 > 3) || (4 <= 2); The test (4 <= 2) is not performed! • Example of useful case: p = (x != 0) && ((y / x) == 0); Avoid division by 0, since ((y / x) == 0) is not performed...
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This note was uploaded on 08/24/2011 for the course CS 106A taught by Professor Sahami,m during the Spring '08 term at Stanford.

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07a-Expressions-rema - || “or” p || q true if p or q(or both are true boolean p =(x!= 1 ||(x!= 2 p is always true you really want boolean p

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