C++ linked list , stack ( sort of ) - c++

Question

#include <iostream>
using namespace std;
struct Node
{
int item; // storage for the node's item
Node* next; // pointer to the next node
};
/**************
use reference
**************/
void addNode(Node*& head, int data , int& count)
{
Node * q; // new node
q = new Node; // allocate memory for the new mode
q->item = data; // inserting data for the new node
q->next = head; // point to previous node ?? how would i do that? ( am i doing it correctly?)
count++; // keep track of number of node
head = q;
}
int main()
{
int a, count = 0;
int data;
char callen;
Node *head = NULL;
do
{
cout << "please enter the data for the next node" << endl;
cin >> data;
addNode(head, data, count);
cout << "do you wish to enter another node? (enter true or false)" << endl;
cin >> callen;
}while( callen != 'n' );
// assuming this is the print function
while(head != NULL)
{
cout << "output" << head->item << endl;
head = head->next; //next element
}
system("pause");
return 0;
}
I tried adding a new element in the list how would i move the head around like a LIFO memory (stack) so the last element is on the very top..
Any help would be appreciated ! The pointers and the nodes are messing with my brain lately ....

Answer 1

In the do-while loop try this
addNode(data, count, head);
instead of
addNode( data, count );
Also, change the signature of addNode as follows:
void addNode( int data , int& count , Node*& head)

Answer 2

The code shouldn't compile because you are using the variable head in addNode but head is local to main.

Answer 3

You could use std::stack for LIFO.
int main()
{
int a, count=0;
int data;
bool repeat;
stl::stack<int> lifo;
// assuming it is an empty list at the beginning and crating a new node below
cout << "enter some data" << endl;
cin >> a ;
lifo.push(a);
do
{
cout << "please enter the data for the next node" <<endl;
cin >> data;
lifo.push(data);
cout << "do you wish to enter another node? (enter true or false)" << endl;
cin >> repeat;
}
while (repeat == true);
// assuming this is the print function
while(!lifo.empty()) {
cout << lifo.pop() << endl;
}
system("pause");
return 0;
}

Answer 4

Sounds like you're trying to learn a bit about link lists. Awesome!
Anyway, I'm not going to give you the exact answer, but I'll give you some pointers in pseudo code, in particular for your addNode member function:
Node* addNode(Node* head, int data, int& count)
{
create a new node
let it point to head
return the pointer to the new node for it to become the new head node
}
int main()
{
// code...
head = addNode(head, data, count);
// more code...
}
As a visual:
head
\/
node A->node B->node C
new node->?
new node
\/
node A->node B->node C

Answer 5

The way you're doing it, by implementing your addNode function as a push operation, already moves the head around, so the head will always point to the last element you added.
Therefore, to implement a function to delete the last element added, you just need to write a simple pop operation: copy the address of the head, make the second element the new head, and release the memory at the copied address:
Node* oldHead = head;
head = head->next;
delete oldHead;
return head;

Answer 6

You could try the following modified code.
#include <iostream>
using namespace std;
struct Node
{
int item; // storage for the node's item
Node* next; // pointer to the next node
};
/**************
use reference
**************/
void addNode(Node*& head, int data , int& count)
{
Node * q; // new node
q = new Node; // allocate memory for the new mode
q->item = data; // inserting data for the new node
q->next = head; // point to previous node ?? how would i do that? ( am i doing it correctly?)
count++; // keep track of number of node
head = q;
}
int main()
{
int a, count = 0;
int data;
bool repeat;
Node *head = NULL;
// assuming it is an empty list at the beginning and crating a new node below
Node *temp;
temp = new Node ;
cout << "enter some data" << endl;
cin >> a ;
temp->item = a;
temp->next = head;
head = temp;
//^^ assuming thats creating the first node ^^
do
{
cout << "please enter the data for the next node" << endl;
cin >> data;
addNode(head, data, count);
cout << "do you wish to enter another node? (enter true or false)" << endl;
cin >> repeat;
}
while (repeat == true);
// assuming this is the print function
temp = head;
while(temp != NULL)
{
cout << "output" << temp->item << endl;
temp = temp->next; //next element
}
return 0;
}