Lecture 05 Loops 2014

8/9/2019 Lecture 05 Loops 2014

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IT101, Semester 1Lecture 5


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Repetition Structure


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Types of Repetition Structures in C++

while

for

do-while

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Pre-test and Post-test loops

Pre-test loops are entrance controlled loops. You execute the loop od! after e"aluatin# thetest.Loop od! can e executed $ero or more times.

Post-test loops are exit controlled loops.

You test the loop after executin# the entire loopod!.

Loop od! can e executed one or more times.

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The While Loop Syntax of While Loop

while (boolean expr)statement;

next statement;

while (boolean expr){

statement 1;statement 2;

}next statement;

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booleanexpr

next statementstatements

false

true


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&xample- Print 'um ersfrom 1 to 10int count (1)while *count +( 10

cout++ count ++endl)count )

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Infinite Loops

%n in nite loop is one in which thecondition is initiall! satis ed, so the loop isentered, ut the condition for exitin# theloop is ne"er met.

enerall! an in nite loop is caused !failin# to modif! a "aria le in"ol"ed in thecondition within the loop od!. To rea2 out of a malfunctionin# pro#rampress ctrl-3 on Linux or ctrl- rea2, on an4 S or 6indows machine.

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What Does This Loop Print

int I =1; while(I < 6 )

cout


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Interacti!e I"# and Loopin$

The sentinel or trailer techni9ue uses aspecial end-of data "alue to indicate the endof meanin#ful data.:sin# the while loop, we place an inputstatement efore the loop to read the rst"alue and an input statement at the ottom ofthe loop to read the next "alue.

The loop condition tests that the "alue is note9ual to the sentinel "alue.

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%n &xample of Sentinel Input

Input a list of positi"e num ers from the2e! oard and nd the a"era#e. The list isterminated with the "alue -;;.

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#include using names ace std;int main()!

int number" sum" cnt; Initiali$ationcout


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Counter 'Controlled Loops

A counter controlled loop is a looping controlstructure in which a loop variable manages the

repetition by counting!he syntax for a counter controlled loop in " and "## is$for(inti expr; boolean expr; increment expr)

statement;

A loop body of more than one statement% must beenclosed in curly braces

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&xamplePrint the num ers from 100 to 10 as follows)100;0 (10 ) I ( i-10

cout++ i ++ ? ? )/

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Comments on the for loop

%ll three expressions that are part of the forloop are optional. The semicolons are notoptional.If the oolean expression is omitted !ou ha"ean in nite loop.:se the for loop when !ou 2now exactl! howman! times the loop od! is to e executed,either as a speci c "alue or as an expression.

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%ll parts of the for loop areoptional

i = *;&or(; i


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)*rea , and )continue, Statements ith Loops

The rea2 statement causes theimmediate termination of the execution of

the loop od! and the continuation ofexecution with the rst statement after theloop.

The continue statement causes theimmediate termination of the execution ofthe loop od! ut not the exitin# of the

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Nestin$ of Loops

The statements in the loop od! ma! e an!3 statement includin# another loopin#statement.6hen a for loop is entered from the top, theinitiali$ation occurs and then the ooleanexpressions are executed.

6hen it is entered as a result of completin#execution of the loop od! the incrementand then the oolean expressions areexecuted.

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Nested (or Loops

&or (I=1; I


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Loop ith Post test .yntax to /o0 hileoop

do

statement; while (bool e0 r);

do!

statement 1;statement ;

while (bool e0 r); 21

statement

boolexpr

3ext statement

true false


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%n example of the Do While Loop

int i=1;do! cout


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Lecture 05 Loops 2014

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Transcript of Lecture 05 Loops 2014