OVERVIEW/REVIEW OF C++
(PART THREE)
======================

do...while loops
----------------
Used to loop ONE or MORE times.

do
{
	// statements that get executed at least once, and are repeated
	//  as long as the logical expression evaluates to true.
}
while ( logical_expression ) ;


As soon as the logical expression evaluates to false, the loop stops
looping (and sequence goes to the first statement after the while statement.)

If the logical expression evaluates to false the FIRST time, the
statements are still executed once, because the expression is not
evaluated until the bottom of the loop.

Using a loop counter:  Counter Controlled Loop

For example, count to 10.

int count = 1 ;		// loop counter variable

do
{
	cout << count << endl ;

	count++ ;		// add one to the count variable
				// same as:  count = count + 1 ;
				// same as:  count += 1 ;
}
while ( count <= 10 ) ;		// counter controlled loop


Example #2, count down:

int count = 10 ;

do
{
	cout << "T minus " << count << endl ;

	count-- ;		// subtract one from the count variable
				// same as:  count = count - 1 ;
				// same as:  count -= 1 ;
}
while ( count > 0 ) ;

cout << "We have lift-off!" << endl ;



Using a loop exit value:  Sentinel Controlled Loop

For example, compute the class average:

int sum = 0 ;				// sum of all grades
int count = 0 ;				// number of grades entered

const int SENTINEL = 999 ;		// loop end value

// NOTE:  The sentinel value must be outside the range of normal
//        data.  If this is not possible, then you must use alternate
//        means (enter data as strings or use end-of-file signals).

int number ;				// single grade

do
{
	cout << "Enter a grade from 0 to 100, 999 to stop: " ;
	cin >> number ;

	if ( number == SENTINEL )
	{
		break ;		// exit the loop 
	}

	if ( ( number < 0 ) || ( number > 100 ) )	// input validation
	{
		cout << number << " is an invalid grade!" << endl ;

		continue ;	// re-start the loop from the top
	}

	sum += number ;		// same as:  sum = sum + number ;
	count++ ;
}
while ( true ) ;

if ( count > 0 )	// prevent division by zero
{
	int average = sum / count ;

	cout << "Class average is " << average << " (from " << count 
	     << " grades)" << endl ;
}
else
{
	cout << "No grades entered." << endl ;
}