Re: Problem with structure and dynamic array

On Wed, 07 May 2008 02:57:31 -0700, curiousEngine wrote:

> how to make provision of a dynamic array say of size 5 with each slot
> holding a structure of type passenger?
> 
> /*
>  * Labsheet   Queues
> Question 1
> Implement a program that shows a queue of people lining at a bus-stop.
> The first one in the queue is the first one to get on the bus. Your
> program should display the following data : Id
> First Name
> Last Name
> DestinationAddress
> The id is to be incremented automatically. By default, it can be set to
> 0.

Does your homework assignment specifically state that you aren't allowed 
to use std::queue? Otherwise, you're re-inventing a (*very* wonky) wheel.

[...]

> Queue::Queue(int MS){
> 	elements = new QueueElementType;

Here you allocate *one* element to 'elements'. I think you probably meant:

elements = new QueueElementType[MS];

> Queue::~Queue(){
> 	delete [] elements;

Here you delete an *array* of elements. This is not going to work.

> void Queue::Enq(QueueElementType apassenger){ 
> 	if (fullqueue())
> 		cout<<"Queue is Full";
> 	else{
> 		Rear = (Rear +1) % MaxQueue;
> 		cout<<"Enter passenger first name:";
> 		cin>> apassenger.first_name;
> 		cout<<endl<<"Enter passenger last name:"; 
cin>>apassenger.last_name;
> 		cout<<endl<<"Enter destination address:"; 
cin>>apassenger.dest_add;
> 		apassenger.id = 1;
> 		elements[Rear] = apassenger; <------

Since you don't allocate an array of elements this is going to access an 
unallocated element. Ditto many other places in your code.

This is a really bad attempt at implementing a queue. Either use 
std::queue (*way* easier) or, if you have to implement it yourself, read 
a good book on data structures (and C++) first - it's tricky.

-- 
Lionel B