1. Chapter 4: Decision Making with Control Structures and Statements JavaScript - Introductory

2. Previewing CartoonQuiz.html File

3. Section A: Decision Making

4. Objectives In this section, students will learn about: if statements if …else statements Nested if statements Switch statements

5. If Statements The process of determining the order in which statements execute in a program is called decision making or flow control The if statement is used to execute specific programming code if the evaluation of a conditional expression returns a value of true Syntax for the if statement is: if (conditional expression) { statement(s); }

6. If Statements The if statement contains three parts: key word if, a conditional expression enclosed within parentheses, and executable statements The statement immediately following the if statement in Figure 4-2 can be written on the same line as the if statement itself

7. If Statements Command block refers to multiple statements contained within a set of braces When an if statement contains a command block, the statements in the block execute when the if statement’s condition evaluates to true Now, if the condition evaluates to false, both statements will be bypassed, since they are contained within a command block

8. If Statements

9. Comparison and Logical Operators with the If Statement

10. Output of CartoonQuiz1.html

11. If … Else Statements When using an if statement, include an else clause to run an alternate set of code if the conditional expression evaluated by the if statement returns a value of false An if statement that includes an else clause is called an if … else statement Consider the else clause a backup plan An if statement can be constructed without the else clause. However, the else clause can only be used with an if statement

12. Nested If and If…Else Statements An if statement contained within an if or if… else statement is called a nested if statement Similarly, an if…else statement contained within an if or if… else statement is called a nested if … else statement Use nested if and if…else statements to perform conditional evaluations in addition to the original conditional evaluation (for example: var numbr = 7; if (number >5) if (number < 10) documnt.writeIn ( “The number is between t and 10.”);

13. Greeting Program with Nested If Statements

14. Modified Greeting Program with Nested If Statements

15. Switch Statements A switch statement controls program flow by executing a specific set of statements, depending on value of an expression The switch statement compares the value of an expression to a label contained within a switch statement If the value matches a particular label, then the statements associated with the label execute The labels within a switch statement are called case labels and mark specific code segments

16. Examples of Case Labels

17. Switch Statements A Case label consists of keyword case, followed by a literal value or variable name, followed by a colon A case label can be followed by a single statement or multiple statements Default label contains statements that execute when the value returned by a switch statement’s conditional expression does not match a case label; keyword is default followed by a colon Break statement is used to exit switch statements and other program control statements

18. Function Containing a Switch Statement

19. Greeting Program Using a Switch Statement

20. Section A: Chapter Summary Flow control is the process of determining the order in which statements are executed in a program The if statement is used to execute specific programming code if the evaluation of a conditional expression returns true A command block refers to multiple statements contained within a set of braces After an if statement’s condition evaluates true, either first statement following condition or command block following condition executes

21. Section A: Chapter Summary Statements following an if statement’s command or command block execute regardless of whether if statement’s conditional expression evaluates true or false The else clause runs an alternate set of code if the conditional expression evaluated by an if statement returns a value of false In an if…else construct, only one set of statements executes: either statement following if statement or statements following the else clause

22. Section A: Chapter Summary An if statement contained within another if statement is called a nested if statement The switch statement controls program flow by executing a specific set of statements; depending on the value returned by an expression Case labels within a switch statement mark specific code segments

23. Section A: Chapter Summary A Default label contains statements that execute when the value returned by switch statement’s conditional expression does not match a case label When a switch statement executes, the value returned by the conditional expression is compared to each case label in the order in which it is encountered A break statement is used to exit a switch statement

24. Section B: Repetition

25. Objectives In this section, students will learn about: while Statements do … while Statements for Statements for … in Statements with Statements continue Statements

26. While Statements Loop statement repeatedly executes a statement or a series of statements while a specific condition is true or until a specific condition becomes true The simplest type of loop statement is the while statement used for repeating a statement or series of statements as long as a given conditional expression evaluates true Each repetition of a looping statement is called an iteration

27. While Statements A Counter is a variable that increments or decrements with each iteration of a loop statement Often name counter variables count, counter, or something similar The following code is an example of a while statement: var count = 1; while (count <= 5) { document.writeIn(count); ++count; }

28. Output of a While Statement Using an Increment Operator

29. Output of a While Statement Using a Decrement Operator

30. While Statements while loop using decrementing counter variables var count = 10; while (count > 0) { document.writeIn (count); --count; } Infinite loop is a situation in which a loop statement never ends because its conditional expression is never updated or false var count = 1; while (count <= 10) { alert (“The number is “ + count); }

31. While Statements The user must force a web browser that is caught in an infinite loop to close by pressing Ctrl+Alt+Delete to access Task List or Manager

32. Output of SpeedLimit.html

33. Do… While Statements Do … while statement executes a statement or statements once, then repeats execution as long as given conditional expression evaluates to true The syntax for do…while statement is as follows: do { statement(s); } while (conditional expression); As with the while statement, include code that changes some part of conditional expression in order to prevent an infinite loop from occurring

34. Examples of a Do … While Statement

35. Days of Week Program in a Web Browser

36. For Statements Use the for statement to loop through code A for statement is used for repeating a statement or series of statements as long as a given conditional expression evaluates true The for statement performs essentially the same function as the while statement: if a conditional expression in for statement evaluates true, the for statement executes repeatedly until it evaluates false

37. For Statements When the JavaScript interpreter encounters a for loop, the following steps occur: –The initialization expression is started –The for loop’s condition is evaluated –If the condition evaluation in Step 2 returns a value of true, then the for loop’s statements execute, Step 4 occurs –The update statement in the for statement’s constructor is executed You can omit any of the three parts of for statement constructor, but must include semicolons to separate each section

38. A For Statement that Displays the Contents of an Array

39. Output of Fast Foods Program

40. Examples of a For Statement

41. Output of CartoonQuizFinal.html

42. For …In Statements for … in statement is a looping statement that executes the same statement or command block for all the properties within an object The syntax for the for… in statement is: for (variable in object) { statement (s); } Unlike other loop statements, the for…in does not require a counter or any other type of code to control how the loop functions

43. A For … In Statement Printing the Names of Properties Within an Object

44. For …In Statements There is no set order or way to control how the properties in an object are assigned to a for…in statement’s variable One benefit of for…in statement is that it enumerates, or assigns an index to, each property in an object

45. Output of SportsCar.html

46. With Statements The with statement eliminates need to retype the name of an object when properties of same object are being referenced in a series The syntax for the with statement is as follows: with (object) { statement(s); } The name of object you want to reference is placed within parentheses following the with keyword

47. Example of a With Statement Assigning Values to Object Properties

48. Continue Statements A Continue statement halts looping statement and restarts the loop with a new iteration Use the continue statement when you want to stop loop for current iteration, but want loop to continue with a new iteration

49. A For Loop with a Continue Statement

50. Output of SportsCar3.html

51. Section B: Chapter Summary A loop statement repeatedly executes statement as long as a specific condition is true or until a specific condition becomes true The while statement is used for repeating a statement or series of statements as long as given conditional expression evaluates true Each repetition of a looping statement is called an iteration A counter is a variable that increments with each iteration of a loop statement

52. Section B: Chapter Summary You must include code that tracks the progress of the while statement and changes the value produced by conditional expression once desired tasks done If a counter variable is beyond range of a while statement’s conditional expression, the while statement is bypassed completely In an infinite loop, a loop statement never ends because its conditional expression is never updated

53. Section B: Chapter Summary The do…while statement executes a statement or statements once, then repeats execution as long as given conditional expression is true The for statement is used for repeating a statement or series as long as a given conditional expression is true You can omit any of the three parts of the for statement constructor, but you must include the semicolon that separates each section The variable name in the for…in statement constructor holds an individual object property

54. Section B: Chapter Summary The for…in statement executes the same statement or command block for all the properties within an object The for…in statement enumerates, or assigns an index to, each property in an object The with statement eliminates the need to retype the name of an object when properties of same object are being referenced in a series The continue statement halts a looping statement and restarts the loop with a new iteration