1 do-while Statement 2 Do-While Statement Is a looping control structure in which the loop condition...

1

do-while Statement

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Do-While Statement

Is a looping control structure in which the loop condition is tested after each iteration of the loop.

SYNTAX

do

{

Statement

} while ( Expression ) ;

Loop body statement can be a single statement or a block.

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Do-While Loop vs. While Loop

POST-TEST loop (exit-condition)

The looping condition is tested after executing the loop body.

Loop body is always executed at least once.

PRE-TEST loop (entry-condition)

The looping condition is tested before executing the loop body.

Loop body may not be executed at all.

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Do-While Loop

When the expression is tested and found to be false, the loop is exited and control passes to the statement that follows the do-while statement.

Statement

Expression

DO

WHILE

FALSE

TRUE

while v. do-while CCL while v. do-while CCL

sum = 0;

counter = 1;

while (counter <= n)

{

sum = sum + counter;

counter++;

}

Pretest Loop

sum = 0;

counter = 1;

do

{

sum = sum + counter;

counter++;

} while (counter <= n)

// Note Sum=1 if n=0

Posttest Loop Loop always executes at

least once

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for Statement

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A Count-Controlled Loop

SYNTAX

for ( initialization ; test expression ; update )

{

0 or more statements to repeat

}

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The for loop contains

an initialization

an expression to test for continuing

an update to execute after each iteration of the body

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Example of Repetition

for ( int num = 1 ; num <= 3 ; num++ )

{

println(num + " Potato");

}

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Example of Repetition num

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

OUTPUT

?

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Example of Repetition num

OUTPUT

1

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

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Example of Repetition num

OUTPUT

1

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

true

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Example of Repetition num

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

OUTPUT

1

1Potato

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Example of Repetition num

OUTPUT

2

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

1Potato

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Example of Repetition num

OUTPUT

2

true

1Potato

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

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Example of Repetition num

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

OUTPUT

2

1Potato

2Potato

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Example of Repetition num

OUTPUT

3

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

1Potato

2Potato

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Example of Repetition num

OUTPUT

3

true

1Potato

2Potato

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

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Example of Repetition num

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

OUTPUT

3

1Potato

2Potato

3Potato

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Example of Repetition num

OUTPUT

4

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

1Potato

2Potato

3Potato

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Example of Repetition num

OUTPUT

4

false

1Potato

2Potato

3Potato

var num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

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Example of Repetition num

When the loop control condition is evaluated and has value false, theloop is said to be “satisfied” and control passes to the statementfollowing the For statement.

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falsevar num;

for ( num = 1 ; num <= 3 ; num++ )

println(num + " Potato");

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The output was:

1Potato2Potato3Potato

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for (var count = 4 ; count > 0 ; count-- )

{

println(count);

}

println(“Done”);

Count-controlled Loop

OUTPUT: 4321Done

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What is output?

for ( var count = 0 ; count < 10 ; count++ )

{

println('*');

}

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OUTPUT

**********

NOTE: the 10 asterisks are all on one line. Why?

Count Control Loop Example

Display integers and their squares from 1 through 10.

for (var i = 1; i <= 10; i++) println(i + " " + i*i);

For example

Display even integers and their squares from 1 through 10.

for (var i = 2; i <= 10; i = i+2) println(i + " " + i*i);

For example

Display integers and their squares from 10 down to 1.

for (var i = 10; i >= 1; i--) println(i + " " + i*i);

For example

Find square roots of 1.1, 1.2, 1.3, ..., 2.0

for (var x = 1.1; x <= 2.0; x =x+0.1)

println(x + " " + sqrt(x));

Compute and return n! = 1 2 3 ... n.

var product = 1;

for (var i = 2; i <= n; i++)

product = product * i;

For example

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What output from this loop?

for (var count = 0; count < 10; count++) ;

{

println(“”);

}

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no output from the for loop! Why? the ; right after the ( ) means that the body

statement is a null statement in general, the Body of the for loop is whatever

statement immediately follows the ( ) that statement can be a single statement, a

block, or a null statement actually, the code outputs one * after the loop

completes its counting to 10

OUTPUT

Display all divisors of each integer from 1

through 50

for (int num = 1; num <= 50; num++)

{

cout << num << " has divisors:\n\t'';

for (int div = 1; div <= num/2; div++)

if (num % div == 0)

cout << div << ", '';

cout << num << endl;

} // See divisors.cpp

Table of 2nTable of 2n

const int tableSize = 20;

long valueSquared = 1;

cout << "n" << " " << "2**n" << endl;

for (int n = 0; n <= tableSize; ++n) {

cout << n << " " << valueSquared << endl;valueSquared = valueSquared * 2;

}

Eliminating WhileExpressionEliminating WhileExpression

The while condition is also optional If omitted the value defaults to true

for ( ; ; )

println("Hi");

while (1)

println("Hi");

Changing the values of any variables involved in the loop condition inside the body of the loop may change the number of repetitions & may result in an infinite loop

for (i = 1; i <= 10; i++)

{

println(i);

i++;

}

Monkeying with LCVs: PPPMonkeying with LCVs: PPP

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Break Statement

break statement can be used with Switch or any of the 3 looping structures

it causes an immediate exit from the Switch, While, Do-While, or For statement in which it appears

if the break is inside nested structures, control exits only the innermost structure containing it

Use break As a Last ResortUse break As a Last Resort

It can become a crutch Think carefully about loop design for loop on right is better

i = 1;

while (1) for (i = 1; i <= 5; i++)

{ println(i);

println(i);

if (i == 5)

break;

i++;

}

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Continue Statement

continue is valid only within loops

terminates the current loop iteration, but not the entire loop

in a For or While, continue causes the rest of the body statement to be skipped--in a For statement, the update is done

in a Do-While, the exit condition is tested, and if true, the next loop iteration is begun