Fall 2008Yanjun Li CSRU JavaScript: Control Statements I Internet & World Wide Web:

Fall 2008Yanjun Li CSRU Control Structures Sequential execution – Statements execute in the order they are written Transfer of control – Next statement to execute may not be the next one in sequence add grade to total total = total + grade; add 1 to counter counter = counter + 1;

Fall 2008Yanjun Li CSRU Boolean Expression Using Equality Operators – x = = y – x != y Using Relational Operators – x > y – x < y – x >= y – x <= y The value of the expression is either true or false

Fall 2008Yanjun Li CSRU if Selection Statement (1) Indicate action only when the condition evaluates to true JavaScript Format: if if ( boolean expression ) statement; Example: if if (grade>= 60) document.writeln(“Passed”); grade >= 60 true false print “Passed”

Fall 2008Yanjun Li CSRU if Selection Statement (2) Multiple actions are performed when the condition is true JavaScript Format: if if ( boolean expression ) { statementOne; statementTwo; : } Example: if if (grade>= 60) { document.writeln(" " + "Congratulations! "); document.writeln(" You Passed! "); }

Fall 2008Yanjun Li CSRU if…else Selection Statement (1) Indicate different actions to be perform when condition is true or false grade >= 60 true print “Failed” false print “Passed”

Fall 2008Yanjun Li CSRU if…else Selection Statement (2) JavaScript Format: if if ( boolean expression ) statement;else JavaScript Example : if ( grade >= 60 ) document.writeln(“Passed”); else document.writeln(“Failed”);

Fall 2008Yanjun Li CSRU if…else Selection Statement (3) Multiple actions JavaScript Format : if if ( boolean expression ) { statementOne; statementTwo; : }else { statementThree; statementFour; : }

Fall 2008Yanjun Li CSRU while Repetition Statement (1) Repetition structure (loop) – Repeat action while some condition remains true. product <= 1000 product = 2 * product true false

Fall 2008Yanjun Li CSRU while Repetition Statement (2) JavaScript Format : initialization; while while ( boolean expression ) { statement; update; } JavaScript Example : var product=2; while ( product <= 1000 ) { document.writeln(product); product = 2 * product; }

Fall 2008Yanjun Li CSRU Counter-Controlled Repetition Counter-controlled repetition – Counter Control the number of times a set of statements executes – Definite repetition

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Fall 2008Yanjun Li CSRU Sentinel-Controlled Repetition Indefinite repetition – Sentinel value

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Fall 2008Yanjun Li CSRU

Fall 2008Yanjun Li CSRU Note on Data Types Loosely typed – Automatically converts between values of different types

Fall 2008Yanjun Li CSRU Web Resources developer.netscape.com/tech/javascript

Fall 2008Yanjun Li CSRU Reference Reproduced from the PowerPoints for Internet & World Wide Web How to Program, 3e by Deitel, Deitel and Goldberg © Reproduced by permission of Pearson Education, Inc.