chapter 05 additionac++l

8/10/2019 Chapter 05 AdditionaC++l

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INTRODUCTION TOC++

Chapter 05: Looping additional

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While Loop for Input Validation

The while loop can be used to create routinesthat repeat until acceptable data is entered

cout number;

while (number < 1 || number > 100)

{ cout number;

}

// Code to use the valid number goes here

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User Control the Loop

Program can be written so that user inputdetermines loop repetition. User is promptedbefore loop. Their input is used to controlnumber of repetitions

Example:

int num, limit;cin >> limit;

num = 1;while (num


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User Control the Loop4

Example:

int num = 1, limit;cout limit;

while (num


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Using do while with menus5

The do-while loop is a good choice for

repeating menu.

Example:

do {

cout


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do while for Input Validation6

Example:

char continue = y; //default value

do {

// other code implementation

cout> continue;

} while ( continue == y || continue == Y);


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5.8 Sentinels

sentinel: value in a list of values that indicates

end of data

Special value that cannot be confused with avalid value, e.g., -999for a test score

Used to terminate input when user may not

know how many values will be entered

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Sentinel Example

int total = 0;cout points;

while (points != -1) // -1 is the sentinel{

total += points;cout > points;

}

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Breaking Out of a Loop

Can usebreakto terminate execution of a

loop

Use sparingly if at all

makes code harder tounderstand

When used in an inner loop, terminates that

loop only and returns to the outer loop

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Using break statement10

int x = 0

while( x < 6)

{

x++;

if ( x == 3)

break;

cout


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5.10 The continueStatement

Can use continueto go to end of loop andprepare for next repetition

whileand do-whileloops go to test and

repeat the loop if test condition is true forloop goes to update step, then tests, and

repeats loop if test condition is true

Use sparingly likebreak, can make

program logic hard to follow

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Using while and continue

statement12

int x = 0

while( x < 6)

{

x++;

if ( x == 3)

continue;

cout


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Using for loop and continue

statement13

for(int x = 0; x < 6; x++){

if ( x == 3)

continue;

cout


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Using continue and break

statement14

int x = 0;

while( x < 6)

{

x++;

if ( x == 5 )break;

if ( x == 3 )

continue;

cout


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5.11 Deciding Which Loop to Use

while: pretest loop (loop body may not beexecuted at all) validating input, sentinelvalue

do-while: post test loop (loop body willalways be executed at least once) repeatinga menu

for: pretest loop (loop body may not beexecuted at all); has initialization and updatecode; is useful with counters or ifprecisenumber of repetitions is known

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chapter 05 additionac++l

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