Re: [Dev-C++] linked list as stack

[Jason H. <jas...@bt...>]

Why is your pop method wrong? I don't really understand why using a node
would be a problem. I assume that you are refering to the node pointer? The
only problem that I can see (at first look) is that initialize doesn't
delete any pointers that may be stored in the stack, but just discards them.
That would be a memory leak.

To use the stack all you need to do is declare an object of stacktype and
call it's members in the usual fasion.

//........... At top of code with other includes
#include "StackHeader.h"

//........... in code body

stacktype MyS;

// push some values onto stack
MyS.push(10);
for(int v = 0; v < 100; v += 5) MyS.push(v);

display(MyS);

add(MyS);

// pop off top value
int x = MyS.pop();

cout << "The value is: " << x << endl;

This code doesn't do anything in particular, it's just a demo.

If I have missed the point please try to explain in a little more detail.

Jason.

----- Original Message -----
From: "chromatonus 712" <chr...@ho...>
To: <dev...@li...>
Sent: Saturday, December 15, 2001 1:57 AM
Subject: [Dev-C++] linked list as stack


> hi, I was given the following header (can't change it, sorry) to write a
> calculator prgm using linked lists as stack (reverse polish notation or
> postfix)
>
> #include <iostream.h>
> #include <conio.h>
>
> struct node
> {
>    int data;
>    node *next;
> };
>
> class stacktype
> {
>    public:
>       // initial-value constructor
>       stacktype( int );
>     // postcondition: initialize list as STACK = NULL
>       // top of stack will be the lead node
>       // and will set screen row to initial value
>       void initialize();
>     // postcondition: object stack list is set to NULL
>       // the screen display is cleared
>       bool is_empty();
>     // postcondition: return FALSE if stack = NULL otherwise
>       // return TRUE
>
>       void push( int );
>       // postcondition: the entered data value will be placed at the HEAD
>       // of the list, making it the TOP.
>       // The second parameter is for the output to the screen
>
>       int pop();
>       // postcondition: the data at the HEAD (top) will be returned, and
the
>       // head will be deleted from the list.
>
>    private:
>       node *mystack;
>       int mytop, my_first_top;
> };
>
>
//==========================================================================
===
> //============================= Free functions
> ================================
>
//==========================================================================
===
> void draw_stack( int );
> // postcondition: draws stack using value from constructor as base value
> void add( stacktype & );
> // precondition: stack must have at least two elements.
> // postcondition: top two elements of stack are popped, added then pushed
> // back onto the stack
> // result  will be displayed in output screen
> void subt( stacktype & );
> // precondition: stack must have at least two elements.
> // postcondition: top two elements of stack are popped, first one
> //                          subtracted from the second and the result
puched
> back
> //                          onto the stack
> // result  will be displayed in output screen
> void mult( stacktype & );
> // precondition: stack must have at least two elements.
> // postcondition: top two elements of stack are popped, multiplied
> //    together, and the product pushed back onto the stack
> // result  will be displayed in output screen
> void display( stacktype );
> // postcondition: the top of the stack will be displayed in the output
> // screen.  This wil be performed after each keystroke.
>
>
> :::::::This was part of what I wrote:
>
//==========================================================================
===
> //============================== Implementation
> ===============================
>
//==========================================================================
===
>
> stacktype::stacktype( int )
> {
>    mystack = NULL;
>    mytop = 0;
>    my_first_top = 0;
> }
> void stacktype::initialize()
> {
>    mystack = NULL;
>    mytop = 0;
>    my_first_top = 0;
>    clrscr();
>    //then it just displays a pretty picture
>    int h, k;
>    gotoxy(3,2);
>    cout<< "> ";
>    for(k=2; k<=22; k++)
>    {
>       gotoxy(60,k);
>       cout<< "||";
>       gotoxy(70,k);
>       cout<< "||";
>    }
>    for(h=60; h<=71; h++)
>    {
>       gotoxy(h,21);
>       cout<< "-";
>       gotoxy(h,22);
>       cout<< "-";
>    }
>    gotoxy(59,22);
>    cout<< "-";
>    gotoxy(72,22);
>    cout<< "-";
>    for(k=3; k<=20; k++)
>    {
>       for(h=62; h<=69; h++)
>       {
>          gotoxy(h,k);
>          cout<< " ";
>       }
>    }
>    gotoxy(50,10);
>    cout<< "OUTPUT:";
>    for(h=50; h<=56; h++)
>    {
>       gotoxy(h,11);
>       cout<< "-";
>       gotoxy(h,14);
>       cout<< "-";
>    }
>    for(k=12; k<=13; k++)
>    {
>       gotoxy(49,k);
>       cout<< "|";
>       gotoxy(57,k);
>       cout<< "|";
>    }
> }
> bool stacktype::is_empty()
> {
>    return (mystack == NULL);
> }
> void stacktype::push( int x )
> {
>    mytop++;
>    node *mm = new node;
>    mm -> data = x;
>    mm -> next = mystack;
>    mystack = mm;
>    gotoxy(62,21-mytop);
>    cout<< x;
>    gotoxy(50,13);
>    cout<< x << "   ";
> }
> int stacktype::pop()
> {
>    gotoxy(62,20-mytop);
>    cout<< "        ";
>    if( !is_empty() )
>    {
>       int x = mystack -> data;
>       mytop--;
>       node *j;
>       j = mystack;
>       mystack = mystack -> next;
>       delete *j;
>       gotoxy(50,13);
>       cout<< x << "   ";
>       return x;
>    }
> }
>
> my pop is wrong because i used nodes, but i don't know how to avoid the
> error, and how would you declare a stacktype using this header? thank you
> very much for your help :)
>
>
>
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