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

for loops
---------
Usually used with a self-contained loop counter, but can be used as
a generic loop.

for ( counter_initialization ; logical_expression ; counter_update )
{
	// statements that get executed as long as the logical expression
	//  evaluates to true.
}

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 skipped, and execution proceeds to below the right
brace.

Using a loop counter:  Counter Controlled Loop

For example, count to 10.

for ( int count = 1 ; count < 11 ; count++ )	// loop counter variable
{
	cout << count << endl ;
}


Example #2, count down:

for ( int count = 10 ; count > 0 ; count-- )
{
	cout << "T minus " << count << endl ;
}

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



Using a loop exit value:  Sentinel Controlled Loop

For example, compute the class average:

int sum ;				// sum of all grades
int count ;				// 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

// NOTE:  count and sum are initialized here, but cannot be declared
//        here, because they are still required after the for loop has
//        completed

for ( count = sum = 0 ; ; )
{
	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++ ;
}

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 ;
}