What is a Queue?

A queue (pronounced like the letter “q”) data structure organizes data in a First In, First Out (FIFO) order: the first piece of data put into the queue is the first piece of data available to remove from the queue. A queue functions just like the line you would get into to go into a ballgame, movie, or concert: the person that arrives first is the first to get into the venue.

Students in a Queue Students in a Queue1

You might be thinking that this sounds a lot like the stack structure we studied a few modules back, with the exception that the stack was a Last in, First Out (LIFO) structure. If so, you are correct. The real difference between a stack and a queue is how we take data out of the data structure. In a stack, we put data onto the top of the stack and removed it from the top as well. With a queue, we put data onto the end (or rear) of the queue and remove it from the start (or front) of the queue.