HELP for doubly linked list
From: drewy2k12 (drewy2k12_at_hotmail-dot-com.no-spam.invalid)
Date: 03/02/04
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Date: 2 Mar 2004 00:19:49 -0600
Heres the story, I have to create a doubly linked list for
class, and i have no clue on how to do it, i can barely create a
single linked list. It has to have both a head and a tail pointer,
and each node in the list must contain two pointers, one pointing
forward and one pointing backwards.
Each node in the list will contain 3 data values: an item ID
(string), a quantity (integer) and a price (float). The ID will
contain only letters and digits – no spaces or other characters (for
example, P123CD). The list must have the following capabilities:
• You must be able to insert a new node at the head of the
list.
• You must be able to insert a new node at the tail of the
list.
• You must be able to output all data in the list to an
arbitrary file stream, one line per node, forward (from head to
tail), followed by a blank line.
• You must be able to output all data in the list to an
arbitrary file stream, one line per node, backward (from tail to
head), followed by a blank line.
Input for the program will come from a file whose name is "Prog-
3.txt". Each line of the file will begin with an op-code that
consists of a single character: H – insert at head, T – insert at
tail, F – display contents forward, B – display contents backwards,
Q – quit. Output will be to a file whose name is the first 4 letters
of your last name, followed by "-3.txt". For example, Meye-3.txt
For example, the data file might contain the following lines:
H P123CD 100 4.95
H T449RS 200 9.95
F
T Q987AB 50 3.00
B
Q
And the output to file would look like:
T449RS 200 9.95
P123CD 100 4.95
Q987AB 50 3.00
P123CD 100 4.95
T449RS 200 9.95
The code i have is this but its not complete and has alot of errors:
#include<iostream>
using namespace std;
class node { // node structure for simple linked list
private:
int data; // data is an integer value
node* link; // pointer to next node in list
string itemid;
int quant;
float price;
public:
node(); //default constructor - makes link null
node(int, int, string, float); //initialization constructor - makes
link null
void setData(int); //assign data value to an existing node
void setLink(node*);//assign link value to an existing node
int getData(); //returns value of data field of node
node* getLink(); //returns value of link field of node
void showData(); // output data value of node (to console)
};
class list {
private:
node* head;
node* tail;
public:
list(); //create an empty list
~list(); //destructor
bool isEmpty(); //returns true if list is empty, false otherwise
void insertHead(node*); //insert referenced node at head of list
void insertTail(node*);
void outputList(); //output all data from list
int sizeOf(); //returns number of nodes in list
};
void buildList(list L); // function to build a list for demo
purposes
//*********************************************************************************************
void main() { // build, output and destroy 3 lists
/* buildList(8);
buildList(5);
buildList(7);
*/
}
//*********************************************************************************************
/*
void buildList(list L) {
list L;
node *p;//define a list
for(int i=1; i<n+1; i++) { //create and insert 4 nodes with data
4, 8, 12, 16
p = new node(4*i);
L.insertHead(p);
}
cout << "The list L contains " << L.sizeOf() << "
nodes." << endl;
L.outputList(); //output data values in list
cout << "***************" << endl;
}
*/
//*********************************************************************************************
node::node(){ //default constructor - makes link null
link = 0;
string itemid = 0;
int quant = 0;
float price = 0;
}
node::node(int d, int q, string id, float p){ //initialization
constructor - makes link null
data = d;
link = 0;
itemid = id;
quant = q;
price = p;
}
void node::setData(int d){ //assign data value to an existing node
data = d;
}
void node::setLink(node* p){//assign link value to an existing node
link = p;
}
int node::getData(){ //returns value of data field of node
return data;
}
node* node::getLink(){ //returns value of link field of node
return link;
}
void node::showData(ostream& out){ // output data value of node
(to console)
out << data << '\t';
}
//**********************************************************************************************
list::list(){ //create an empty list
head = 0;
tail =0;
}
list::~list() {
node* p = head;
while(p!=0) {
head = p->getLink();
delete p;
p = head;
}
}
bool list::isEmpty(){ //returns true if list is empty, false
otherwise
return (head==0);
}
void list::insertHead(node* p){ //insert referenced node at head of
list
if (head == 0){
p->setLink(head);
head = p;
tail = p;
}
else {
p->setLink(head);
head = p;
}
}
void list::insertTail(node* p){
if (tail == 0){
p->setLink(tail);
head = p;
tail = p;
}
else{
p->setLink(tail);
tail =p;
}
}
void list::outputList(){ //output all data from list
node *p=head;
while(p!=0) {
p->showData(); // output data in node
p = p->getLink();
}
cout << endl; // end line of output
}
int list::sizeOf(){ //returns number of nodes in list
node *p=head;
int n=0;
while(p!=0) {
n++;
p = p->getLink();
}
return n;
}
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