Multi Server Queue Simulation C++ - c++

Question

This assignment (I've linked the full description here) asks us to create a multi server queue simulation (i.e. grocery store type scenario). My code seems to be working for the most part however I currently have 2 questions pertaining to my output that I am having a hard time answering.
Why does queue_total not match the actual number of elements displayed in each queue at the end of the program?
Why won't new items be enqueued to the shortest queue even though the shortest_queue function seems to be working?
The main code:
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <iomanip>
#include "queue_2.h"
using namespace std;
// Utility function to return shortest queue.
int shortest_queue(Queue line[], int queuecount)
{
int shortest = 0;
// Condition 1: If a queue is empty
// with no active transactions, return it.
for (int i = 0; i < queuecount; i++) {
if (line[i].empty() && line[i].get_trans_time() == 0)
return i;
}
// Condition 2: If a queue is simply empty,
// return it next.
for (int i = 0; i < queuecount; i++) {
if(line[i].empty()) {
return i;
}
}
// Condition 3: (otherwise) If all queues are
// occupied check for shortest queue.
for (int i = 1; i < queuecount; i++) {
if(line[i].size() < line[shortest].size())
shortest = i;
}
return shortest;
}
// Utility function to return total number
// of customers waiting in queues.
int queue_total(Queue q[], int queuecount)
{
int custcount = 0;
for (int i = 0; i < queuecount; ++i)
custcount += q[i].size();
return custcount;
}
int main()
{
// Variable decelrations
int trans_time = 0;
int count = 0;
int entry_time;
int wait_sum = 0;
int wait_time = 0;
int seed = 3;
int ariv_prob = 80;
int MAX_TRANS_TIME = 12;
int DURATION = 120;
int queuecount = 4;
int shortline;
int temp;
// Create a list of queues
// and random number generator
Queue line[queuecount];
srand(seed);
for (int time = 1; time < DURATION + 1; time++)
{
// Display the time
cout << "Time: " << time << endl;
// Check probablity only once per iteration
if ( rand() % 100 < ariv_prob ) {
shortline = shortest_queue(line, queuecount);
line[shortline].enqueue(time);
}
// Update the transaction times for
// the corresponding queues and compute
// summary statistics.
for (int i = 0; i < queuecount; i++) {
if ( line[i].get_trans_time() == 0 ) {
if ( !line[i].empty() ) {
entry_time = line[i].print_front();
line[i].dequeue();
temp = (time - entry_time);
if(temp > wait_time)
wait_time = temp;
wait_sum += (time - entry_time);
++count;
line[i].set_trans_time((rand() % MAX_TRANS_TIME) + 1);
}
}
// Decrement and update transaction time.
else {
trans_time = line[i].get_trans_time() - 1;
line[i].set_trans_time(trans_time);
}
}
// Display status of the queues for the
// the given iteration.
for (int i = 0; i < queuecount; i++) {
cout << setw(4) << line[i].get_trans_time() << " ";
line[i].display();
}
cout << endl;
}
cout << count << " customers waited an average of ";
cout << wait_sum / count << " ticks." << endl;
cout << "The longest time a customer waited was " << wait_time << " ticks." << endl;
cout << queue_total(line, queuecount) << " customers remain in the lines." << endl;
return 0;
}
The queue implementation
#ifndef QUEUE_H
#define QUEUE_H
#include <iostream>
using namespace std;
class Queue {
private:
struct Node {
int data;
Node* next;
Node(int d) {
data = d;
next = NULL;
}
};
Node* front;
Node* rear;
int count;
int trans_time;
public:
Queue() {
front = rear = NULL;
count = trans_time = 0;
}
void enqueue(int x) {
// Create a new linked Node.
Node* temp = new Node(x);
// If the queue is already empty
// then new node is front and rear
if (empty()) {
front = rear = temp;
return;
}
// Add the new node at the end
// of the queue and change the rear
rear->next = temp;
rear = temp;
++count;
}
void dequeue() {
// If the queue is empty
// then we can return NULL
if (empty())
return;
// Store the previous front and
// move the front one node ahead
Node* temp = front;
front = front->next;
// If front becomes NULL, then
// Change the rear to be NULL as well
if (front == NULL)
rear = NULL;
delete(temp);
--count;
}
// Utility function to check
// if the queue is empty
bool empty() {
return (front == NULL && rear == NULL);
}
int size() {
return count;
}
// Utility function to print front
// element of the queue
int print_front() {
return front->data;
}
void display() {
Node* temp = front;
while (!(temp == NULL)) {
cout << temp->data << " ";
temp = temp->next;
}
cout << endl;
}
void set_trans_time(int i) {
trans_time = i;
}
int get_trans_time() {
return trans_time;
}
};
#endif

Answer 1

Your enqueue function doesn't increment (or set) the count when inserting into an empty queue. This causes the count to be 0 for a queue with 1 element.
The comparisons for count > 0 or count >= 0 before decrementing/incrementing it should be unnecessary. If those conditions are ever false then you have a problem elsewhere that caused the inconsistency.