Chapter 05 Part III

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Chapter 05 (Part III)

• Control Statements Part II

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Objectives

• In this part you will learn
• To understand multiple selection using the switch
  selection statement.
• To use the break and continue program control
  statements to alter the flow of control.

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5.6 switch Multiple-Selection Statement

• switch statement
• Used for multiple selections
• Tests a variable or expression

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5.6 switch Multiple-Selection Statement

• switch statement
• Controlling expression
• Expression in parentheses after keyword switch
• case labels
• Compared with the controlling expression
• Statements following the matching case label are
  executed
• Braces are not necessary around multiple
  statements in a case label

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The Use of switch Statement

• int option
• cin gtgt option
• switch (option)
• case 0
• break
• case 1
• break
• default
• break

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5.6 switch Multiple-Selection Statement

• default case
• Executes if no matching case label is found
• This case is optional
• If no match and no default case
• Control simply continues after the switch
• A break statements causes execution to proceed
  with the first statement after the switch
• Without a break statement, execution will fall
  through to the next case label

Note Forgetting a break statement when one is
needed in a switch statement is a logic error.
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5.6 switch Multiple-Selection Statement

• The default clause does not require a break
  statement. Some programmers include break for
  clarity and for symmetry with other cases.
• Specifying an expression in the case label is a
  syntax error.
• Incorrect example
• switch (option)
• case ab
• break

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Fig. 5.12 switch multiple-selection statement
with break statements.
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Comparison
int option cin gtgt option if (option 1)
result a b else if (option 2)
result a b else cout ltlt Incorrect
option! ltlt endl
int option cin gtgt option switch (option)
case 1 result a b break case
2 result a b break default
cout ltlt Incorrect option! ltlt endl break
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Calculating number of letters
Examples of character constant A, b, C,
\n
Note Do not confuse string constant with
character constant. A string is a sequence of
characters. String A Character A
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Reading character input

• Function cin.get()
• Reads one character from the keyboard
• EOF
• End-of-file.
• Defined in ltiostreamgt
• ltctrlgt d in UNIX/Linux
• ltctrlgt z in Windows and then press Enter.
• while ((letter cin.get()) ! EOF)
• Read one character from keyboard and assign it to
  letter.
• Compare letter with EOF
• If letter ! EOF (End-of-file), enter the loop.
• Otherwise (letter EOF), leave the loop.

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switch Multiple-Selection Statement
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Output Results
Character constant
String constant

• Note
• A character constant is enclosed using single
  quotation marks.
• We can also represent a character constant using
  integer type.
• A string constant is enclosed using double
  quotation marks.

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Integer Data Types

• Integer data types
• short
• Abbreviation of short int
• Minimum range is -32,768 to 32,767
• long
• Abbreviation of long int
• Minimum range is -2,147,483,648 to 2,147,483,647
• int
• Equivalent to either short or long on most
  computers
• char
• Can be used to represent small integers

Note Integer data types can vary in size between
systems
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5.7 break and continue Statements

• break/continue statements
• Alter flow of control
• break statement
• Causes immediate exit from control structure
• Used in while, for, dowhile or switch statements
• Example
• int option 0
• while (option ! -1)
• cin gtgt option
• if (option -1)
• break //force immediate exit

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5.7 break and continue Statements

• continue statement
• Skips remaining statements in loop body
• Proceeds to increment and condition test in for
  loops
• Proceeds to condition test in while/dowhile
  loops
• Then performs next iteration (if not terminating)
• Used in while, for or dowhile statements

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Loop 10 times
Exit for statement (with a break) when count
equals 5
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Loop 10 times
Skip line 14 and proceed to line 9 when count
equals 5
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Performance Tip 5.5

• The break and continue statements, when used
  properly, perform faster than do the
  corresponding structured techniques.