C++ Control Technique Repetition

8/6/2019 C++ Control Technique Repetition

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BITG 1113:BITG 1113:

Control TechniqueControl Technique(Repetition)(Repetition)

LECTURE 5


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Ability to repeat an operation or a series of operations

manytimes.

An action or a series of actions.

C++ has threerepetition

, or looping structures thatallow us to repeat a set of statements until certain

conditions are met:

while

do-while for

Why is Repetition Needed ?Why is Repetition Needed ?

BITG 1113 : LECTURE 5


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whilewhile LoopingLooping StructureStructure

4BITG 1113 : LECTURE 5


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whilewhile LoopLoop



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int count = 0;

while (count < 2)

{

cout


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int count = 0;

while (count < 2)

{

cout


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int count = 0;

while (count < 2)

{

cout


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int count = 0;

while (count < 2)

{

cout


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int count = 0;

while (count < 2)

{

cout


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int count = 0;

while (count < 2)

{

cout


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int count = 0;

while (count < 2)

{

cout


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int count = 0;

while (count < 2)

{

cout


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int count = 0;

while (count < 2)

{

cout


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ControllingControlling whilewhile LoopLoop

When a program needs to be tested again and again on

certain data it will operate a large amount of data.

To overcome the problem, we have four cases:

Counter controlled while loops Sentinel controlled while loops

Flag controlled while loops

User controlled while loops

EOF-Controlled while loops



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CounterCounter--controlledcontrolled whilewhile loopsloops

We know how many pieces of data need to be read.

Use a counter, by initializing the value to 0.

Ifcounter < N, the body of the while statement

executes until the value ofcounter >= N

The structure :

counter = 0; //initialize the loop control variablewhile (counter < N) //test the loop control variable{

counter ++//update the loop control variable

}



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ExampleofaExampleofawhilewhile loop : Counterloop : Counter--controlledcontrolled


#include

using namespace std;

int main ()

{

double score, sum=0,average;

int studProc;

studProc = 0; //initialization

while (studProc < 10) //condition

{

cout >score;

sum += score;

studProc++; //updating

}

average = sum/10;

cout


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We do not know how many data needs to be read

.

The last entry called sentinel, is a special value.

A sentinel value is a value that is not a legitimate data value

for a particular problem (but is of proper type) that is used

as a stopping value.

The while loop continues to execute as long as the

program has not read the sentinel.

General structure :cin >> variable;

while (variable != -1){

cin>>variable;

}

SentinelSentinel--ControlledControlled whilewhile loopsloops

Sentinel Value



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ExampleofaExampleofawhilewhile loop : Sentinelloop : Sentinel--controlledcontrolled



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ExampleofaExampleofawhilewhile loop : Sentinelloop : Sentinel--controlledcontrolled



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Uses a user predefined variable to control the loop

User ControlledUser Controlled whilewhile LoopsLoops

char continueLoop = 'Y';

while (continueLoop == 'Y')

{

// Execute body once// Prompt the user for confirmation

cout > continueLoop;

}



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ExampleofaExampleofawhilewhile loop : Userloop : User--controlledcontrolled


#include


int main ()

{

int count=0;

double score, sum=0,average;

char answer=y; //initialization

while (answer==y|| answer==Y) //condition

{ cout >score;

sum += score;

count++;coutanswer; //updating

}

average = sum/count;

cout


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Output

Enter your score:60

Do you want to continue?y/Y for Yes:y

Enter your score:50


Enter your score:90


Enter your score:80

Do you want to continue?y/Y for Yes:yEnter your score:55

Do you want to continue?y/Y for Yes:n

The average is :67

ExampleofaExampleofawhilewhile loop : Userloop : User--controlledcontrolled



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Uses a bool variable to control the loop Example :

found =false;//initialize the loop controlvariable

while (!found) //test the loop control variable{

if (expression)found = true //re-initialize the loop control

variable

}

FlagFlag--ControlledControlled whilewhile LoopsLoops



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ExampleofaExampleofawhilewhile loop : Flagloop : Flag--controlledcontrolled

#include


int main()

{

char letter;

bool found = false;//initializationwhile (!found) //condition

{

coutletter;

if (letter=='x')

{found = true; //updating

cout


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Output

Enter a letter. Press x to stop : s

Enter a letter. Press x to stop : x

STOP

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ExampleofaExampleofawhilewhile loop : Flagloop : Flag--controlledcontrolled



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Is used when the data file is frequently altered, added ordeleted

Example :

cin >> variable; //initialize the loop control

variable

while (cin)

{

cin >> variable; //re-initialize the loop

control variable

}

The loop stops when the system detects the end-of-file

signal( by pressing ).

EOFEOF--ControlledControlled whilewhile LoopsLoops



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#include


int main( )

{

int n = 0;

float sum = 0;

cout n)

sum += n;cout


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Output :

Enter your numbers:^Z to stop.

1 2 3 4 5 ^Z

SUM = 15

Press any key to continue . . .

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ExampleofaExampleofawhilewhile loop :EOFloop :EOF--controlledcontrolled



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dowhiledowhile Looping StructureLooping Structure



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dowhiledowhile LoopLoop



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dowhiledowhile LoopLoop

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#include


int main()

{

int a; //initialization

do

{

cout > a; //updating

} while (a < 10 || a > 20); //condition

cout


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Output :Output :

To stop enter a number between 10 & 20 : 3

To stop enter a number between 10 & 20 : 10

END



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forfor Looping StructureLooping Structure



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forfor LoopLoop



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int i;

for (i = 0; i < 2; i++)

{

cout


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TraceTrace forfor Loop, Cont.Loop, Cont.

int i;

for (i = 0; i < 2; i++)

{

cout


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int i;

for (i = 0; i < 2; i++)

{

cout


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int i;

for (i = 0; i < 2; i++)

{

cout


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int i;

for (i = 0; i < 2; i++)

{

cout


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int i;

for (i = 0; i < 2; i++)

{

cout


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int i;

for (i = 0; i < 2; i++)

{

cout


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int i;

for (i = 0; i < 2; i++)

{

cout


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int i;

for (i = 0; i < 2; i++)

{

cout


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int i;

for (i = 0; i < 2; i++)

{

cout


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ComparingComparing forfor andand whilewhile LoopsLoops



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ComparingComparing forfor andand whilewhile LoopsLoops

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int sum = 0;

intint ii = 1= 1;

while (ii a;

sum += a;

ii++++;

}

sum = 0;

for(intint ii = 1= 1; ii a;

sum += a;

}



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intint ii = 2= 2;

while (ii


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RecommendationsRecommendations

Use the one that is most intuitive and comfortable for you.

In general, a for loop may be used if the number of

repetitions is known, as, for example, when you need to

print a message 100 times.

Awhile loop may be used if the number ofrepetitions is

not known, as in the case of reading the numbers until the

input is 0.

Ado-while loop can be used to replace a while loop if

the loop body has to be executed before testing thecontinuation condition.



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NestedNested forfor LoopLoop

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// Print numbers on a line

#include #include

int main (void)

{

for (int i = 1; i


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Other Statement Related to LoopingOther Statement Related to Looping

break

causes a loop to terminate

terminate only the inner loop in nested loop

continue

transfers to the testing expression in while and

dowhile statement

transfers to the updating expression in a for

statement.


ThTh ii SS


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while (limit test)

{

continue;

}

do

{

continue;

} while (limit test)

for (initialize;limit test;update)

{

continue;

}

TheThe continuecontinue StatementStatement



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TheThe breakbreak ExampleExample

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int main ( )

{int x = 5 ;

while ( x < = 20)

{

if (x == 10 )

break;

cout


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TheThe continuecontinue ExampleExample

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#include


int main( )

{

int count = 0;

int n = 0;

float sum = 0;

cout n)

{

if (n == 0)

continue;

sum += n;

count++;

}

cout


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OutputOutput

Enter some numbers. Press ^Z to stop.

2

0

3

^Z

Sum/Count = 2.5

56BITG 1113 LECTURE 5

C++ Control Technique Repetition

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