Chapter 4: Decision Making with Control Structures and Statements

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Chapter 4 Decision Making with Control
Structures and Statements

• JavaScript - Introductory

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Previewing CartoonQuiz.html File
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• Section A
• Decision Making

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Objectives

• In this section, you will learn about
• if statements
• if else statements
• Nested if statements
• Switch statements

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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)

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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

Examples\Example4_2.html
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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
  statements condition evaluates to true
  (condition is satisfied)
• Now, if the condition evaluates to false, both
  statements will be bypassed, since they are
  contained within a command block

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If Statements
Examples\Example4_3.html
Examples\Example4_4.html
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Comparison and Logical Operators with the If
Statement
Examples\Example4_5.html
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Output of CartoonQuiz1.html
Examples\CartoonQuiz1.html
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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

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Nested If and IfElse Statements

• An if statement contained within an if or if
  else statement is called a nested if statement
• Similarly, an ifelse statement contained within
  an if or if else statement is called a nested if
  else statement
• Use nested if and ifelse statements to perform
  conditional evaluations in addition to the
  original conditional evaluation (for
  example var numbr 7 if (number
  gt5) if (number lt 10)
  documnt.writeIn ( The number is between t
  and 10.)

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Greeting Program with Nested If Statements
Examples\Example4_8.html
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Modified Greeting Program with Nested If
Statements
Examples\Example4_9.html
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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

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Examples of Case Labels
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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 statements
  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

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Function Containing a Switch Statement
Examples\Example4_11.html
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Greeting Program Using a Switch Statement
Examples\Example4_12.html
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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 statements condition evaluates true,
  either first statement following condition or
  command block following condition executes

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Section A Chapter Summary

• Statements following an if statements command
  or command block execute regardless of whether if
  statements 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 ifelse construct, only one set of
  statements executes either statement following
  if statement or statements following the else
  clause

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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

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Section A Chapter Summary

• A Default label contains statements that execute
  when the value returned by switch statements
  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

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