1. Conditinoal Constructs Review
what is a block? what is special about declaring a variable inside a block? what is a scope of a variable?
what are conditional constructs? what type of conditional constructs have we studied?
what is nested if?
what is multiway-if? How does multiway-if relate to nested if?
what is a switch statement? is it better than multiway-if?
what does break inside switch do?
what is conditional operator? conditional assignment? what construct can be used instead?
what is programming idiom?
what is a unary, binary, ternary operator?

2. Iterative Constructs
while, for, do-while

3. Iterative Constructs provide
ability to execute the same code multiple times
three constructs
while statement
do-while statement
for statement

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

5. The do-while Statement
while (n != 0 ) { cin >> n; if (n > max) max = n; }
The do-while Statement
syntax do
body
while (expression);
semantics
execute body
if expression is true then do another iteration
iterate until expression evaluates to false
example
int max=0, n;
do {
cin >> n;
if (n > max) max = n;
} while (n == 0);
body
expression
true
false

6. The for Statement initStatement false expression true body
postStatement
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 << "i is " << i << endl;
loop variable - declared inside for
its scope is body of the loop
modifying loop variable inside body is poor style, use while instead

7. Iterate and Keep Track Idiom
what is idiom again?
often need to iterate while keep track of some value across iterations – maximum value found, sum, if all positive, etc.
idiom
before loop, declare tracking variable to keep track, initialize it
what is initialization again?
inside loop, update tracking variable, use branching if necessary to examine
after loop, use the tracking variable that accumulated the result
example:
cout << "Input number [0 to quit]: ";
int max, n;
cin >> n; max = n;
while (n != 0 ) {
cin >> n;
if ( n > max) max = n; }
cout << ”Maximum number: ” << max << endl;

8. Break and Continue with Iterative Constructs
break - exits innermost loop
int sum=0;
while(sum < 100) {
int i; cin >> i;
if (i< 0) {
cout << ”found negative number\n”;
break; }
sum +=i;
continue - skip the remaining statements and start a new iteration (evaluate expression)
for (int i = 0; i < 20; ++i) { int intVar; cin >> intVar;
if(intVar < 0) continue;
avoid break/continue with loops as they make code less readable (make regular loop exit unnecessary)
first try to code loop without them

9. Nesting of Iterative Constructs
iterative constructs can be nested: one iterative construct may be inside the body of another
example:
for (int i = 0; i < 10; ++i) // outer loop
for (int j = 0; j < 10; ++j) // inner loop
cout << i << j << endl;
what would this code output?
note, there is no need for curly brackets
nesting may be more than two loops deep
for/while/do-while can be mixed in nesting
besides nested loops, loop body may contain other code
including branching constructs: a branching construct nested in the loop

10. Iteration Key Points
make sure there is a statement that will eventually falsify the looping construct expression (i.e., the loop must stop)
make sure that all counters and tracking variables are initialized
have a clear purpose for the loop
good way to know if you do: can write clear comments above loop