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while, for, do-while

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provide ability to execute the same code multiple times

three constructs while statement

do-while statement

for statement

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syntaxwhile

(expression)

action semantics

if expressionis truethen execute action

repeat this process untilexpressionevaluates tofalse

actionis either asingle statement or ablock

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expression

action

true false

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syntaxdoaction

while(expression);

semantics execute action if expressionis true

then execute actionagain

repeat this process untilexpressionevaluates tofalse

actionis either a singlestatement or a block

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action

true

false

expression

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syntaxfor(init_statement;expression;post_statement)

action semantics

execute init_statement evaluate expressionif true

execute action execute post_statement repeat

examplefor (int i = 0; i < 20; ++i)

cout

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what is idiom again?

often need to iterate while keep track of some value across

iterationsmaximum found, sum, if all positive, etc.

idiom

before loop declare variable to keep track, initialize it

inside loop, update tracking variable, use branching ifnecessary to examine

after loop, use the tracking variable that accumulated theresult

example:

cout > n; max = n;

while (n != 0 ) {cin >> n;

if ( n > max) max = n;

}

cout

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break- exits innermost loop

int sum=0;while(sum < 100) {

int i; cin >> i;if (i< 0) {

cout > intVar;

if(intVar < 0) continue;sum +=i;}

avoid break/continuewith loops as they make code less readable (avoidregular loop exit) first try to code loop without them

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iterative constructs can be nested: oneiterative construct may be inside the body ofanother

example:for (int i = 0; i < 10; ++i) // outer loopfor (int j = 0; j < 10; ++j) // inner loop

cout

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key points make sure there is a statement that will

eventually nullify the iteration criterion (i.e.,the loop must stop)

make sure that initialization of any loopcounters or iterators is properly performed

have a clear purpose for the loop

document the purpose of the loop and how thebody of the loop advances the purpose of the loop

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