Lesson 7.1 repitition structure

© 2016 Cengage Learning®. May not be scanned, copied or
Introduction to Programming in C++
Eighth Edition
Lesson 7.1:
The Repetition Structure
duplicated, or posted to a publicly accessible website, in whole
or in part.

• Differentiate between apretest loop and aposttestloop
• Include apretest loop in pseudocode
• Include apretest loop in aflowchart
• Codeapretest loop using the C++whilestatement
• Utilize counter and accumulator variables
• Codeapretest loop using the C++forstatement
or in part.
2An Introduction to Programming with C++, Eighth Edition
Objectives

• Therepetition structure, or loop, processes one or
more instructions repeatedly
• Every loop contains aBoolean condition that controls
whether the instructions arerepeated
• Alooping condition sayswhether to continue looping
through instructions
• Aloop exit condition sayswhether to stop looping
through the instructions
• Every looping condition can be expressed asaloop exit
condition (its opposite)
or in part.
Repeating Program Instructions

• C++useslooping conditions in repetitionstructures
• Arepetition structure can be pretest orposttest
• In apretest loop, the condition is evaluated beforethe
instructions in the loop areprocessed
• In aposttest loop, the condition is evaluated after the
instructions in the loop areprocessed
• In both cases,the condition is evaluated witheach
repetition
or in part.
(cont’d.)

• Theinstructions in aposttest loop will alwaysbe
processed at least once
• Instructions in apretest loop may not beprocessed if
the condition initially evaluates tofalse
• Therepeatable instructions in aloop are called the loop
body
• Thecondition in aloop must evaluate to aBoolean
value
or in part.
(cont’d.)

(cont’d.)
Figure 7-1 A problem that requires the sequence and
selection structures
or in part.

(cont’d.)
Figure 7-2 A problem that requires the sequence and repetition structures
or in part.

• Most loops have acondition and aloop body
• Someloops require the user to enter aspecialsentinel
value to end theloop
• Sentinel values should be easily distinguishable from
the valid data recognized by theprogram
• When aloop’s condition evaluates to true,the
instructions in the loop bodyare processed
• Otherwise, the instructions are skipped andprocessing
continues with the first instruction after the loop
or in part.
Using a Pretest Loop to Solve a Real-
World Problem

• After each processing of the loop body (iteration), the
loop’s condition is reevaluated to determine if the
instructions should be processedagain
• Aprimingread is an instruction that appears before a
loop and is used to set up the loop with an initial value
entered by the user
• An update read is an instruction that appears within a
loop that allows the user to enter a new value at each
iteration of theloop
or in part.
World Problem (cont.)

World Problem (cont’d.)
Figure 7-3 Problem specification and IPO chart for the commission program
or in part.

Figure 7-4 Components of Algorithm 2 from Figure 7-3
World Problem (cont’d.)
or in part.

• Thediamond symbol in aflowchart is the decision
symbol – represents repetition structures
• Adiamond representing arepetition structure contains
aBoolean condition
• Thecondition determines whether the instructionsin
the loop areprocessed
• Adiamond representing arepetition structure hasone
flowline leading into it and two leading out
or in part.
Flowcharting a Pretest Loop

• Theflowlines leading out are marked “T” (true)and “F”
(false)
• The“T” line points to the loop body
• The “F” line points to the instructions to be processed if
the loop’s condition evaluates tofalse
• Theflowline entering the diamond and symbolsand
flowlines of the true path form a circle, or loop
• Thisdistinguishes arepetition structure from a
selection structure in aflowchart
or in part.
Flowcharting a Pretest Loop (cont’d.)

Figure 7-5 Flowchart for algorithm shown in Figure 7-4
or in part.

Figure 7-6 First sales entry recorded in the desk-check table
Figure 7-7 First salesperson’s entry in the desk-check table
or in part.

Figure 7-8 Second salesperson’s entry in the desk-check table
Figure 7-9 Completed desk-check table
or in part.

• Youcan usethe while statement to code apretest
loop in C++
• Syntax is:
while (condition)
one statement or a statement block to beprocessedas
long asthe condition istrue
• Must supply looping condition (Booleanexpression)
• condition can contain constants, variables, functions,
arithmetic operators, comparison operators, andlogical
operators
or in part.
The while Statement

• Must also provide loop body statements, whichare
processed repeatedly aslong ascondition is true
• If more than one statement in loop body, must be
entered asastatement block (enclosed in braces)
• Caninclude braces even if there is only onestatement
in the statementblock
• Good programming practice to include acomment,
such as//end while, to mark the end of the while
statement
or in part.
The while Statement (cont’d.)

• Aloop whose instructions are processed indefinitely is
called an infinite loopor endlessloop
• Youcan usually stop aprogram that hasentered an
infinite loop by pressingCtrl+c
or in part.

Figure 7-10 How to use the while statement
or in part.

Figure 7-11 IPO chart information and C++ instructions for the
commission program
or in part.

Figure 7-12 A sample run of the commission program
or in part.

Lesson 7.1 repitition structure

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