Examples of the two types of loops

Event-controlled loop

• depends on an event to happen to stop the loop
• uses trailer/sentinel logic
• can handle any amount of data, from none at all to huge amount
• you do not know when the event will happen ahead of the time you start executing the loop

Trailer logic pattern

	priming read/input
	while (event hasn't happened)
	{
		process the data received
		read/input
	}

common errors with an event-controlled loop

• forgetting the priming read
• reversing the test
• forgetting the second read
• putting the second read anywhere but the bottom of the loop

Counter-controlled loop

• depends on a counter
• you know how many times you want the body of the loop to be executed ahead of time
• does not use sentinel logic exactly

  Counter pattern

  	set counter to initial value
  	while (counter relation limit)
  	{
  		process data as needed
  		increment (decrement) the counter
  	}
  

  common errors with a counter-controlled loop

  • forgetting to initialize the counter
  • putting the initialization inside the loop
  • forgetting the counting statement
  • not testing the counter against the limit
  • using a relation that causes the loop to go one time too many (<=) instead of <