btkr1343 - chapter 4b - control technique -repetition

8/19/2019 BTKR1343 - Chapter 4b - Control Technique -Repetition

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Chapter 4b

Repetition Control Structure


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The Objectives

1. To use while, do-while, and for loops toexecute statements repeatedly.

2. To understand the o! o" control in loops.

#. To use $oolean expressions to control loops.4. To !rite nested loops.

%. To &no! the similarities and di'erences o"three types o" loops.

(. )Optional* To implement pro+ram control!ith break and continue.


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hy is Repetition -eeded

• /bility to repeat an operation or a serieso" operations many times.

• /n action or a series o" actions.

• C00 has three repetition , or loopin+structures that allo! us to repeat a set o"statements until certain conditions aremet• while

• do-while

• for


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while oopin+ Structure4


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while Loop


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Trace whileoop

int count = 0;

!hile )count 3 2*

count 33 5elcome to C0067

count007

8

9nitiali:e count


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Trace whileoop

int count = 0;

!hile )count 3 2*


count007

8

)count 3 2* is True


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Trace whileoop

int count = 0;

!hile )count 3 2*


count007

8

;rint elcome to C00


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Trace whileoop

int count = 0;

!hile )count 3 2*


count007

8

9ncrease count by 1-O count is 1


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Trace whileoop

int count = 0;

!hile )count 3 2*


count007

8

)count 3 2* is still truesince count is 1


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Trace whileoop

int count = 0;

!hile )count 3 2*


count007

8

;rint elcome to C00


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Trace whileoop

int count = 0;

!hile )count 3 2*


count007

8

9ncrease count by 1-O count is 2


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Trace whileoop

int count = 0;

!hile )count 3 2*


count007

8

)count 3 2* is "alsesince -O count is 2


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Trace whileoop

int count = 0;

!hile )count 3 2*


count007

8

The loop exits.


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Controllin+ while oop

• hen a pro+ram needs to be tested a+ain anda+ain on certain data it !ill operate a lar+eamount o" data.

•

To overcome the problem, !e have "our cases Counter controlled !hile loops

Sentinel controlled !hile loops

=la+ controlled !hile loops

>ser controlled !hile loops


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Counter-controlled whileloops

• e &no! ho! many pieces o" data need to be read.

• >se a counter, by initiali:in+ the value to @.

• 9" counter 3 -, the body o" the !hile statementexecutes until the value o" counter AB -

• The structure

counter = 0; //initializethe loop control variable

while (counter< N) //testthe loop control variable

{…

…

counter ++ //updatethe loop control variable

…

}


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Output


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Sentinel?Controlled whileloops

• e do not &no! ho! many data needs to be read.

• The last entry called sentinel, is a special value.

• / sentinel value is a value that is not a le+itimate data value"or a particular problem )but is o" proper type* that is used as

a 5stoppin+6 value.• The !hile loop continues to execute as lon+ as the pro+ram

has not read the sentinel.

• Feneral structure cin variable;

while (variable != "#)

{

…

cinvariable;

…

}/entinel alue


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>ser Controlled while oops

• >ses a user predeGned variable tocontrol the loop

char continueoop B HIH7

!hile )continueoop BB HIH*

JJ


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=la+?Controlled while oops

• >ses a bool variable to control the loop

•


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doAwhile oopin+ Structure


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doAwhile Loop


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doAwhile oop

Ninclude 3iostreamA

usin+ namespace std7

int main)*

int a7JJinitiali:ation

do

cout 33 KTo stop enter a number bet!een 1@ 2@ K7

cin AA a7 JJupdatin+8 !hile )a 3 1@ a A 2@*7 JJcondition

cout 33K


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Output

To stop enter a number bet!een 1@ 2@ #

To stop enter a number bet!een 1@ 2@ 1@


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for oopin+ Structure


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for Loop


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Trace for oop

int i

"or )iB@7 i327 i00*

cout 33 5elcome to C00678

declare i


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Trace for oop

int i

"or )i=07 i327 i00*


execute

initiali:er-O i is @


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Trace for oop

int i

"or )iB@7 i


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Trace for oop

int i

"or )iB@7 i327 i00*


;rintelcome to C00


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Trace for oop

int i

"or )iB@7 i327 i,,*



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Trace for oop

int i

"or )iB@7 i


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Trace for oop

int i

"or )iB@7 i327 i00*


;rintelcome to C00


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Trace for oop

int i

"or )iB@7 i327 i,,*



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Trace for oop

int i

"or )iB@7 i


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Trace for oop

int i

"or )iB@7 i327 i00*



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Comparin+ for and whileoops

C i f d hil


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Comparin+ for and whileoops


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Comparing while dowhile for loops


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Decommendations

• >se the one that is most intuitive andcom"ortable "or you.

• 9n +eneral, a for loop may be used i" thenumber o" repetitions is &no!n, as, "or example,!hen you need to print a messa+e 1@@ times.

• / while loop may be used i" the number o"repetitions is not &no!n, as in the case o"readin+ the numbers until the input is @.

• / do-while loop can be used to replace a !hileloop i" the loop body has to be executed be"oretestin+ the continuation condition.


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-ested for oop


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Other Statement Related to oopin+

• break causes a loop to terminate

terminate only the inner loop in nested

loop• continue

trans"ers to the testin+ expression in

!hile and doU!hile statement trans"ers to the updatin+ expression in a

"or statement.


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The continue Statement


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The break


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Output

btkr1343 - chapter 4b - control technique -repetition

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