c++ linked list problems - c++

Question

#include "node.h"
#include <iostream>
// List class
class List
{
node *head; // head is an object that stores the address of the first node
public:
// constructor that initializes every list to null
List()
{
head = NULL;
}
// prtototype of the list member functions
void Print();
void Insert(float sal, int en);
void Delete(float sal, int en);
};
//linklist.h above
#include "linklist.h"
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
/**
* Append a node to the linked list
*/
void List::Insert(float sal, int en)
{
// Create a new node
node* newNode = new node();
newNode->SetData(sal, en);
newNode->setNext(NULL);
// Create a temp pointer
node *tmp = head;
if ( tmp != NULL )
{
// Nodes already present in the list
// Parse to end of list
/*while ( tmp->Next() != NULL )
{
tmp = tmp->Next();
}*/
// Point the last node to the new node
tmp->setNext(head);
}
else
{
// First node in the list
head = newNode;
}
}
/**
* Delete a node from the list
*/
void List::Delete(float salary, int data)
{
// Create a temp pointer
node *tmp = head;
// No nodes
if ( tmp == NULL )
return;
// Last node of the list
if ( tmp->Next() == NULL )
{
delete tmp;
head = NULL;
}
else
{
// Parse thru the nodes
node *prev;
do
{
if ( tmp->Epnum() == data && tmp->Salary()== salary )
break;
prev = tmp;
tmp = tmp->Next();
} while ( tmp != NULL );
// Adjust the pointers
prev->setNext(tmp->Next());
// Delete the current node
delete tmp;
}
}
/**
* Print the contents of the list
*/
void List::Print()
{
// Temp pointer
node *tmp = head;
// No nodes
if ( tmp == NULL )
{
cout << "EMPTY" << endl;
return;
}
// One node in the list
if ( tmp->Next() == NULL )
{
cout << tmp->Salary() + tmp->Epnum();
cout << " --> ";
cout << "NULL" << endl;
}
else
{
// Parse and print the list
do
{
cout << tmp->Epnum();
cout << " --> ";
tmp = tmp->Next();
}
while ( tmp != NULL );
cout << "NULL" << endl;
}
}
//linlist.cpp above
#include <iostream>
#include <cstdlib>
#include "linklist.h"
using namespace std;
void menu(List &);
int main()
{
// New list
List list;
menu(list);
return 0;
}
void menu(List &list)
{ char choice;
int item;
float salary;
do{
system("CLS"); // use #include <cstdlib>
cout << "\t\t\tMain Menu\n\n";
cout << "\tInsert{A}\n";
cout << "\tDelete\n";
cout << "\tPrint{P}\n";
cout << "\tExit\n";
cout << "\t\t What? ";cin >>choice;
choice = toupper(choice);
cin.ignore();
switch (choice)
{ case 'A':
cout << "Enter Employee numbers to insert and salary : "; cin >> item; cin>>salary;
list.Insert(salary, item);
cout << item<< " Inserted \n"; cin.get();
break;
/*case 'D':
cout << "Enter Item to Delete : "; cin >> item;
list.Delete(item);
cout << item<< " Deleted\n";cin.get();
break;*/
case 'P':
list.Print();cin.get();
break;
}
}while (choice != 'E');
}
//main.cpp above
//node.h
//#ifndef NODE_H
#define NODE_H
//node class
class node {
int epnum;
float salary;
node* next;
public:
node()
{} //null constructor
//stores argument passed in func.
void SetData(float _salary, int _epnum){
salary = _salary;
epnum = _epnum;
}
//stores in next the address of the next node
void setNext (node* anext){
next = anext;
}
//returns epnum stored
int Epnum(){
return epnum;
}
float Salary(){
return salary;}
//returns addres of next node
node* Next(){
return next;
}
};
//node.h above
I need to create a linked list that inserts a node at the front of the list as a program and of course print it out. I am unable to insert the node at the front of the list for some reason and I run into an infinte loop while trying to print it. It does something but I do not know exactly what. Please help.

Answer 1

In List::Insert, you have:
node *tmp = head;
followed by
tmp->next = head;
Hence, you have circular link in the object. Its next points to itself. This leads to infinite loop in the print function.
What you need is very simple:
void List::Insert(float sal, int en)
{
// Create a new node
node* newNode = new node();
newNode->SetData(sal, en);
newNode->setNext(head);
head = newNode;
}

Answer 2

In your insert method when you have 1 element already present tmp is set to head, then tmp->setNext(head); will create a reference to itself. This is the reason of infinite loop in your print method. Try the following insert code instead.
void List::Insert(float sal, int en)
{
// Create a new node
node* newNode = new node();
newNode->SetData(sal, en);
newNode->setNext(head);
head = newNode;
}
I would also note that in you print method there is no corner case for the list with 1 element. Your loop will perfectly handle this case. You will get the same result if you omit One node in the list branch.
void List::Print()
{
// Temp pointer
node *tmp = head;
// No nodes
if ( tmp == NULL )
{
cout << "EMPTY" << endl;
return;
}
// Parse and print the list
do
{
cout << tmp->Epnum();
cout << " --> ";
tmp = tmp->Next();
}
while ( tmp != NULL );
cout << "NULL" << endl;
}

Answer 3

void List::Insert(float sal, int en)
{
// Create a new node
node* newNode = new node();
newNode->SetData(sal, en);
newNode->setNext(NULL);
//set the newNode next to point to head
newNode->setNext(head);
//set the new head as the newNode
head = newNode;
// Create a temp pointer
//node *tmp = head;
/*if ( tmp != NULL )
{
// Nodes already present in the list
// Parse to end of list
/*while ( tmp->Next() != NULL )
{
tmp = tmp->Next();
}
// Point the last node to the new node
tmp->setNext(head);
}
else
{
// First node in the list
head = newNode;
}*/
}
/**
* Delete a node from the list
*/
void List::Delete(float salary, int data)
{
// Create a temp pointer
node *tmp = head;
// No nodes
if ( tmp == NULL )
return;
// Last node of the list
if ( tmp->Next() == NULL )
{
delete tmp;
head = NULL;
}
else
{
// Parse thru the nodes
node *prev;
do
{
if ( tmp->Epnum() == data && tmp->Salary()== salary )
break;
prev = tmp;
tmp = tmp->Next();
} while ( tmp != NULL );
// Adjust the pointers
prev->setNext(tmp->Next());
// Delete the current node
delete tmp;
}
}
/**
* Print the contents of the list
*/
void List::Print()
{
// Temp pointer
node *tmp = head;
// No nodes
if ( tmp == NULL )
{
cout << "EMPTY" << endl;
return;
}
// One node in the list
if ( tmp->Next() == NULL )
{
cout << tmp->Salary() + tmp->Epnum();
cout << " --> ";
cout << "NULL" << endl;
}
else
{
// Parse and print the list
do
{
cout << tmp->Epnum();
cout << " --> ";
tmp = tmp->Next();
}
while ( tmp != NULL );
cout << "NULL" << endl;
}
}
nvm i was tired when i was writting this code and just realized what I did wrong.