CSCI 270 Programming Assignment #3 Summer 2005
Due: Thursday, July 14
Emphasis: Queues
As we mentioned in class there are many variations on the basic queue data type, including priority
queues, dequeus, etc. Another example of a queue variation is the random queue. In a random queue,
items are added to the back of the queue as normal. However, when an item is removed from the
queue, instead of taking the item at the front of the queue we instead remove a random item from the
queue (with equal probability of removing any item that is currently on the queue).
Modify the Queue class remove() method to implement a random queue. You may use either the array
or linked list versions of the Queue class as your starting point. Either choice will make some things
easy to do, but present some problems for other things. For example, when you randomly remove an
item from the middle of an array based implementation, you need to do something about the hole left
behind. For the linked list version, you need to do some work to find the item selected at random,
unlike the array based method where you can directly access the item randomly chosen.
You should use a random function, like the rand() function in the C standard library, to choose the item
to remove. The standard library function rand() returns a random number such that 0 <= rand() <
32767.
To convert this into a number within a specific range 1 .. n , use the algorithm rand() % n + 1 .
For instance, if we were simulating rolling dice, we would want a number in the range 1 .. 6, so we
could code something like: die = rand() % 6 + 1 .
To obtain a number within the range 0 .. n , use the algorithm rand() % (n + 1) .
The random number generator is initialized (needs to be called only once) by a call to the standard
library function srand() . You can pass srand a specific value (good for testing purposes until you're
sure your program is working correctly), or you can initialize it with a value from the system clock (for
a random starting seed):
srand (237); or srand (unsigned (time (NULL)));
To use the rand and srand functions, include stdlib.h (or cstdlib), and to use the time function, include
time.h (or ctime).
With the random queue class you just implemented, write a client that picks numbers for a lottery.
Your client should put the numbers 1 through 99 on your random queue. Then it should print the
results of the lottery by removing five items and displaying the winning numbers.
Requirements
1) You must start with either the array or linked list versions of the Queue as presented in the book, it
is your choice.
2) You need only modify the dequeue() member function to remove an item at random from the
queue elements (rather than removing item from the head of the queue).
