Chapter 4 Decision Making with Control Structures and

Chapter 4: Decision Making with Control Structures and Statements Java. Script - Introductory

Previewing Cartoon. Quiz. html File

Section A: Decision Making

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

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); }

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

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

If Statements

Comparison and Logical Operators with the If Statement

Output of Cartoon. Quiz 1. html

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

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. write. In ( “The number is between t and 10. ”);

Greeting Program with Nested If Statements

Modified Greeting Program with Nested If Statements

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

Examples of Case Labels

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

Function Containing a Switch Statement

Greeting Program Using a Switch Statement

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

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

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

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

Section B: Repetition

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

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

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. write. In(count); ++count;

Output of a While Statement Using an Increment Operator

Output of a While Statement Using a Decrement Operator

While Statements • while loop using decrementing counter variables var count = 10; while (count > 0) { document. write. In (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); }

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

Output of Speed. Limit. html

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

Examples of a Do … While Statement

Days of Week Program in a Web Browser

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

For Statements • When the Java. Script 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

A For Statement that Displays the Contents of an Array

Output of Fast Foods Program

Examples of a For Statement

Output of Cartoon. Quiz. Final. html

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

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

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

Output of Sports. Car. html

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

Example of a With Statement Assigning Values to Object Properties

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

A For Loop with a Continue Statement

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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

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

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

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