displaying elements of stack?

[Vish0203]

Hi,
I wrote the following program for stacks using linked list! But, the display function doesn't seem to work!
can anyone point out the errors in this?
Thankyou!

#include <iostream>
#include <cstdlib>
#include <iomanip>
using namespace std;
template <class T>
class stack
{
    T data;
    stack<T> *top;
    stack<T> *next;
    public:
        stack()
        {
            top = NULL;
            next = NULL;
        }
        void push();
        void pop();
        void display();
};

template <class T>
void stack<T> :: push()
{
    T elepu;
    stack<T> *temp = new stack;
    cout<<"Enter the element to be pushed: ";
    cin>>elepu;
    temp -> data = elepu;
    if(top == NULL)
    {
      top = temp;
      top -> next = NULL;   
    }
    else
    {
      top -> next = temp;
      top = temp;
      top -> next = NULL;
    }
    cout<<endl<<"Element pushed!"<<endl;
}

template <class T>
void stack<T> :: pop()
{
    stack<T> *temp = new stack;
    temp = top;
    if(top == NULL)
    {
        cout<<"Stack Underflow"<<endl;
    }
    else
    {
        temp -> data = top -> data;
        top = top -> next;
        delete temp;
    }
    cout<<endl<<"Element popped!"<<endl;
}

template <class T>
void stack<T> :: display()
{
    cout<<"Elements in stack are: "<<endl;
    stack<T> *temp = new stack;
    temp = top;
    if(top == NULL)
    {
        cout<<"Stack is Empty";
    }
    else
    {
        while(temp -> next != NULL)
        {
            cout<<temp -> data<<setw(6);
            temp = temp -> next;
        }
    }
}

int main()
{
    char choice;
    stack<int> S;
    while(1)
    {
    cout<<setw(6)<<"MENU"<<endl<<" ^^^^^"<<endl
        <<" [1] PUSH"<<endl
        <<" [2] POP"<<endl
        <<" [3] DISPLAY"<<endl
        <<" [4] EXIT"<<endl;
    cout<<"\nENTER YOUR CHOICE: ";
    cin>>choice;
    switch(choice)
     {
        case '1': S.push(); break;
        case '2': S.pop(); break;
        case '3': S.display(); break;
        case '4': exit(0); break;
        default: cout<<"Not a valid entry!!" ; break;
     }
      cout<<endl<<"Do you wish to continue? (Y/N) ";
      if(cin.get() == 'Y' || cin.get() == 'y')
        continue;
      else
        break;  
    }
    cin.ignore();
    cin.get();
    return 0;   
}

[deceptikon]

Your push() member function is broken. In the case where top isn't NULL, you have three lines:

top -> next = temp;
top = temp;
top -> next = NULL;

The first thing to notice is that top->next is always reset to NULL, always. That line is a bug and should be removed. You're also pushing in the wrong direction. The top of the stack is the most recently pushed item, so you need to set temp->next to top rather than top->next to temp:

temp -> next = top;
top = temp;

The display member function also has an off by one error wherein you don't print the oldest node in the stack. Your condition should check temp against NULL rather than temp->next:

while(temp != NULL)

[Vish0203]

works fine now! Thanks.. :)

[umesh314]

#include <iostream>
#include <cstdlib>
#include <iomanip>
using namespace std;
template <class T>
class stack
{
    T data;
    stack<T> *top;
    stack<T> *next;
    public:
        stack()
        {
            top = NULL;
            next = NULL;
        }
        void push();
        void pop();
        void display();
};

template <class T>
void stack<T> :: push()
{
    T elepu;
    stack<T> *temp   = new stack;
    stack<T> *temp_1 = new stack;
    cout<<"Enter the element to be pushed: ";
    cin>>elepu;
//  temp -> data = elepu;
    if(top == NULL)
    {
//    top = temp;
      top = new stack;
      top -> data = elepu;
      top -> next = NULL;   
    }
    else
    {
      temp = top;
      while(temp -> next != NULL)
      temp = temp -> next;
      temp -> next = temp_1;
      temp_1 -> next = NULL;
      temp_1 -> data = elepu; 
    }
    cout<<endl<<"Element pushed!"<<endl;
}

template <class T>
void stack<T> :: pop()
{
    stack<T> *temp = new stack;
    temp = top;
    if(top == NULL)
    {
        cout<<"Stack Underflow"<<endl;
    }
    else
    {
    while( temp -> next -> next != NULL )
        temp = temp -> next;
        temp -> next = NULL;
//      temp -> data = top -> data;
//      top = top -> next;
//      delete temp;
    }
    cout<<endl<<"Element popped!"<<endl;
}

template <class T>
void stack<T> :: display()
{
    cout<<"Elements in stack are: "<<endl;
    stack<T> *temp = new stack;
    temp = top;
    if(top == NULL)
    {
        cout<<"Stack is Empty";
    }
    else
    {
        while(temp != NULL)
        {
            cout<<temp -> data<< endl;
            temp = temp -> next;
        }
    }
}

int main()
{
    char choice;
    stack<int> S;
    while(1)
    {
    cout<<setw(6)<<"MENU"<<endl<<" ^^^^^"<<endl
        <<" [1] PUSH"<<endl
        <<" [2] POP"<<endl
        <<" [3] DISPLAY"<<endl
        <<" [4] EXIT"<<endl;
    cout<<"\nENTER YOUR CHOICE: ";
    cin>>choice;
    switch(choice)
     {
        case '1': S.push(); break;
        case '2': S.pop(); break;
        case '3': S.display(); break;
        case '4': exit(0); break;
        default: cout<<"Not a valid entry!!" ; break;
     }
      cout<<endl<<"Do you wish to continue? (Y/N) ";
      if(cin.get() == 'Y' || cin.get() == 'y')
        continue;
      else
        break;  
    }
    cin.ignore();
    cin.get();
    return 0;   
}