6- iterative constructs: while, do-while, for

Question 1

increment

Answer 1

increase value by one, unary operator: ++

Question 2

decrement

Answer 2

decrease value by one, unary operator: –

Question 3

Iterative Constructs

Answer 3

provide ability to execute the same code multiple times
1. while statement
2. do-while statement
3. for statement

Question 4

while

Answer 4

syntax
while (expression)
body
semantics
if expression is true then execute body
body is either a single statement or a block
iteration: single execution of body
iterate until expression evaluates to false
example
while (n != 0) {
cin&raquo_space; n;
if (n > max) max = n;
}

Question 5

do-while

Answer 5

syntax
do
body
while (expression);
semantics
execute body
if expression is true then iterate again
iterate until expression evaluates to false
example
int max=0, n;
do {
cin&raquo_space; n;
if (n > max) max = n;
} while (n != 0);

Question 6

for

Answer 6

syntax
for(initStatement;
expression; postStatement)
body
semantics
execute initStatement
evaluate expression, if true: iterate
iteration:
execute body
execute postStatement
repeat expression evaluation
example
for (int i=0; i<20; ++i)
cout &laquo_space;“i is “ &laquo_space;i &laquo_space;endl;
loop variable - declared inside for
its scope is body of the loop
modifying loop variable inside body is poor style, use while instead

Question 7

break

Answer 7

exits innermost loop
avoid break with loops as they make code less readable (makes regular loop exit unnecessary): first try to code loop without it

Question 8

continue

Answer 8

skip the remaining statements and start a new iteration (evaluate expression)