Pointer in C++ isn't initialized correctly - c++

Question

I'm trying to execute the following code, everything is fine except one thing and that is tellerArray[2] is never initialized properly, it always creates problems for me, and I don't why. It creates problem for me: I came to know this fact when I debugged the code multiple times.
#include <iostream>
#include <stddef.h>
using namespace std;
class Customer {
public:
void setTime(int time) { this->_time = time; }
int getTime() { return this->_time; }
void setNextCustomer(Customer *next) { this->_next = next; }
Customer* getNextCustomer() { return this->_next;}
private:
int _time;
Customer *_next;
};
class Teller {
public:
Teller();
~Teller();
void addCustomer(Customer *customer);
int totalCustomers();
int totalTime();
private:
Customer *head;
Customer *tail;
};
Teller::Teller() {
this->head = NULL;
this->tail = NULL;
}
Teller::~Teller() {
delete head;
delete tail;
head = NULL;
tail = NULL;
}
void Teller::addCustomer(Customer *customer) {
customer->setNextCustomer(NULL);
if(head == NULL) {
head = customer;
} else {
tail->setNextCustomer(customer);
}
tail = customer;
}
int Teller::totalTime() {
int totalTime = 0;
Customer *tempCust = new Customer;
for(tempCust = head; tempCust != NULL; tempCust = tempCust->getNextCustomer()) {
totalTime += tempCust->getTime();
}
return totalTime;
}
int Teller::totalCustomers() {
int totalCustomers = 0;
Customer *tempCust = new Customer;
for(tempCust = head; tempCust != NULL; tempCust = tempCust->getNextCustomer()) {
totalCustomers += 1;
}
return totalCustomers;
}
int getLeast(int, int, int, int);
int getMax(int, int, int, int);
int main(int argc, const char*argv[]) {
Teller *tellerArray[4];
// creating four tellers ( counters )
Teller *tellerOne = new Teller();
Teller *tellerTwo = new Teller();
Teller *tellerThree = new Teller();
Teller *tellerFour = new Teller();
tellerArray[0] = tellerOne;
tellerArray[1] = tellerTwo;
tellerArray[2] = tellerThree;
tellerArray[3] = tellerFour;
char wannaBuyAnother = 'n';
int duration = 0, minTime = 0, maxTime = 0, index = 0;
do {
cout<<"Enter duration of your transaction: ";
cin>>duration;
Customer *customer = new Customer;
customer->setTime(duration);
minTime = getLeast( tellerOne->totalTime(),
tellerTwo->totalTime(),
tellerThree->totalTime(),
tellerFour->totalTime() );
for(index = 0; index < 4; index++) {
if( (tellerArray[index]->totalTime()) == minTime ) {
break;
}
}
tellerArray[index]->addCustomer(customer);
cout<<"You can stand in Queue "<<index + 1<<"\n";
cout<<"Do you want to buy another Ticket(Y/N)? ";
cin>>wannaBuyAnother;
} while ( wannaBuyAnother == 'y' || wannaBuyAnother == 'Y' );
cout<<"Number of Customers Deal By Every Teller\n";
for(index = 0; index < 4; index++) {
cout<<"T"<<index<< "= \t"<<tellerArray[index]->totalCustomers()<<"\n";
}
maxTime = getMax( tellerOne->totalTime(),
tellerTwo->totalTime(),
tellerThree->totalTime(),
tellerFour->totalTime() );
for(index = 0; index < 4; index++) {
if( (tellerArray[index]->totalTime()) == maxTime ) {
cout<<"TELLER "<<index+1<<" Deal Maximum Customers of the Day\n";
break;
}
}
return 0;
}
int getLeast(int first, int second, int third, int fourth) {
int min = first;
if( second < min ) {
min = second;
} else if ( third < min ) {
min = third;
} else if ( fourth < min ) {
min = fourth;
}
return min;
}
int getMax(int first, int second, int third, int fourth) {
int max = first;
if( second > max ) {
max = second;
} else if ( third > max ) {
max = third;
} else if ( fourth > max ) {
max = fourth;
}
return max;
}
Here is output when I debug my code.
tellerArray[0] Teller * 0xbffff308
tellerArray[1] Teller * 0x8048c64
tellerArray[2] Teller * 0x1
tellerArray[3] Teller * 0xffff
What my code is actually doing is using a linked list ( customer class ) to create a queue ( teller class ) and then based upon the time of each queue, it determines in which queue to put the next customer?

Answer 1

The initialisation looks fine. Those values are odd, but unless you have a specific debug build, you can't always rely on a reported pointer value being correct. However, it's possible they are being corrupted because of the following undefined behaviour in your program:
I notice that you never initialise the _next pointer on Customer to NULL, nor to you set it when you add it to the list. So your list tail always has an undefined _next pointer. This is very likely to give you problems.
You should create a default constructor on Customer and initialise _next to NULL.
One unrelated thing I will mention is that your getLeast and getMax functions do not work. Why don't you try this:
cout << getLeast(4, 3, 2, 1) << endl;
cout << getMax(1, 2, 3, 4) << endl;

Answer 2

The code is a bit bizarre, I don't see how the code matches the description of what it is supposed to do.
But bugs aren't hard to find, look at this code
int Teller::totalTime() {
int totalTime = 0;
Customer *tempCust = new Customer;
for(tempCust = head; tempCust != NULL; tempCust = tempCust->getNextCustomer()) {
totalTime += tempCust->getTime();
}
return totalTime;
}
At no point does your code set a value for tempCust->_next so tempCust->getNextCustomer() returns a garbage value and so from this point all bets are off, and your code could end up doing anything.
Frankly I can't see any logic to your code so I'm not sure what to do to fix it. At the very least I'd advise to to set _next to NULL in the Customer constructor.
class Customer {
public:
Customer() { this->_next = NULL; }
...
private:
...
Customer *_next;
};