Array Of Linked Lists (5 Queues) - c++

Question

I would like to implement an array of linked lists to create a printing queue; with an array of five queues. Each queue is meant to represent a user printing a job sent to the printer.
This is the code I currently have:
#include "stdafx.h"
#include <iostream>
using namespace std;
struct node
{
float value;
struct node *next;
};
node *head = NULL;
node* A[5];
int insertNodes(node *head, int value)
{
node *aNode, *Ptr;
aNode = new node;
aNode->value = value;
aNode->next = NULL;
if (head == NULL)
head = aNode;
else
{
Ptr = head;
while (Ptr->next != NULL)
Ptr = Ptr->next;
Ptr->next = Ptr;
}
return head;
}
int _tmain(int argc, _TCHAR* argv[])
{
int num;
for (int i = 0; i < 5; i++)
{
cout << "Insert number";
cin >> num;
A[i] = insertNodes(i, num)
}
return 0;
}
This code does not work as intended, as I am unable to add "jobs" to the queues.
Where have I gone wrong?

Answer 1

There is a number of issues with your code:
You are programming in C++, not C, so instead of struct node *next you should simply write node *next.
Your insertNodes function returns a pointer to the head of the list, so you need to return node*, not int.
When you insert into a list with an existing head, you never insert the item. You have to do Ptr->next = aNode, not Ptr->next = Ptr.
In your main function, you are expected to pass a pointer to the head of the list to insertNodes, but you actually pass it an int. Instead, try A[i] = insertNodes(A[i], num).
You store float in your list nodes, but input int - is that actually desired?
However, since you are in C++, you can probably avoid most of these pitfalls entirely by relying on what the standard library already provides.
Simply #include <deque> and you can use everything that std::deque (a double-ended queue) provides, including push_back to add elements at the end, front to access the first element, and pop_front to remove it - a real queue, no need for custom linked lists:
#include "stdafx.h"
#include <deque>
#include <vector>
#include <iostream>
std::vector<std::deque<float>> A {5};
int _tmain(int argc, _TCHAR* argv[])
{
float input;
for (int i = 0; i < 5; i++)
{
std::cout << "Insert number: ";
std::cin >> input;
A[i].push_back(input);
}
return 0;
}