Problem with structure and dynamic array

[curiousEngine]

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
DestinationAddr ess
The id is to be incremented automatically. By default, it can be set
to 0.
*
* IMPLEMENTATION USING AN ARRAY
*/
#include <iostream>
using namespace std;

struct passenger{
int id;
char first_name[15];
char last_name[30];
char dest_add[20];
};

typedef passenger QueueElementTyp e;

class Queue{
private:
QueueElementTyp e * elements;
int MaxQueue;
int Front;
int Rear;
int fullqueue();
int emptyqueue();
public:
Queue(int MS);
void Enq(QueueElemen tType apassenger);
QueueElementTyp e Deq();
void printQueue();
~Queue();
};

Queue::Queue(in t MS){
elements = new QueueElementTyp e;
MaxQueue = MS;
Front = MaxQueue -1;
Rear = MaxQueue -1;
}

Queue::~Queue() {
delete [] elements;
MaxQueue = 0;
Front = MaxQueue -1;
Rear = MaxQueue -1;
}

int Queue::fullqueu e(){
return(Front = (Rear + 1) % MaxQueue);
}

int Queue::emptyque ue(){
return (Front == Rear);}

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

QueueElementTyp e Queue::Deq(){
QueueElementTyp e mypass;
if (emptyqueue())
cout<<"Queue is empty";
else{
Front = (Front + 1) % MaxQueue;
mypass = elements[Front];
}
return(mypass);
}

void Queue::printQue ue(){
for(int i = Front ; i<= Rear; i++){
cout<<elements[i].id;
cout<<elements[i].first_name;
cout<<elements[i].last_name;
cout<<elements[i].dest_add;
}
}
int main(int argc, char** argv)
{
Queue myqueue(5);
QueueElementTyp e mypass;
myqueue.Enq(myp ass);
myqueue.printQu eue();

myqueue.Enq(myp ass);
myqueue.printQu eue();
return 0;
}

[Lionel B]

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
DestinationAddr ess
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(in t MS){
elements = new QueueElementTyp e;

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

elements = new QueueElementTyp e[MS];

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

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

void Queue::Enq(Queu eElementType apassenger){
if (fullqueue())
cout<<"Queue is Full";
else{
Rear = (Rear +1) % MaxQueue;
cout<<"Enter passenger first name:";
cin>apassenger. first_name;
cout<<endl<<"En ter passenger last name:";

cin>>apassenger .last_name;

cout<<endl<<"En ter 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