Thread: C++ stack using class

Originally Posted by Elysia

I would make pop return the element that is removed and rename top to peek. I don't know why they did it like this in STL, but frankly, it's annoying and peek/pop is pretty much standard anyway.
And StainedBlue, as we have already tried to explain, the OP should not be using dynamic memory at this point. A stack does not need dynamic memory. A vector or a deque should suffice here. Let's not try to put out different solutions here. It will only serve to confuse.

Why not just make a vector wrapper, and forget manual memory management all together then?

EDIT: By that I mean, why does the OP have a pointer at all?

Originally Posted by StainedBlue

EDIT: By that I mean, why does the OP have a pointer at all?

That is what we're trying to remove.

And that is why we're cautioning you to use a vector. Too much complexity otherwise.
We have already told you that realloc should not be used with new/delete.

And what exactly is reallok?

im trying to reallocate memory for the stack but it seems that im doing it wrong, is this a correct way to reallocate memory for a simple array?

Code:

#include <iostream>

using namespace std;

int *reallok(int *x,int &size){
    int *y;
    size = size+2;
    y = new int[size];
    int i;
  //  cout<<x[0]<<x[1]<<endl;
  //  cin.get();
    for (i=0;i<size-2;i++){
        y[i] = x[i];
        }
    for(i;i<size;i++){
                      y[i] = 0;
                      }
    delete x;
    return y;
}

    
int main(void){
    
    int *a = new int[2];
    int *check;
    int size = 2;
    
    
    a[0] = 0;
    a[1] = 1;
    check = reallok(a,size);
    if(check!=NULL){
                    a = check;
                    cout<<"success"<<endl;
                   cout<<a[0]<<" "<<a[1]<<" "<<a[2]<<" "<<a[3]<<endl; //prints 0 1 0 0
                    }
  
    cin.get();
    
    return 0;
}

im thinking of doing something similar, but im doing it wrong, i tried to do the same thing in my class, but i get errors

i ll create another simple class to see what exactly im doing wrong, but i think that if i achieve this, the whole app will be working correctly, or not?

Yes, just use std::vector:

Code:

#include <vector>
#include <algorithm>

int main()
{
    std::vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);
    v.push_back(4);
    std::for_each(v.begin(), v.end(), [](int n) { std::cout << n << std::endl; });
}

And then fix your indentation.

thanks for the alternative solution, but sadly i dont know anything about vectors yet & my professor used realloc malloc and free in his program

i ll be taking exams in 3 days and was just curious how this could be implemented using C++ code without vectors becauwe we havent done them yet

i think i have it correct now

let me explain the code in detail

stack.h has the class

Code:

class stack{
      
      private:
              int *x;
              int pos,size;
    
      public:
             stack();
             stack(int n);
             stack(stack &other);
             bool pop(int &element);
             bool push(int element);
             bool isempty();
             int *reallok(int*,int&);
             
      };

here i declare a variable *x which is the dynamic array that i create for the stack

then i have 3 constructors, the first one has no parameters and it creates an array of 10 elements which i can increace later on

then pop gets the element that is in pos-1 position, push puts a new element on top, isempty checks if the stack is empty

i forgot about the third constructor which i dont use at all, it just creates a new "copy" stack

in main.cpp i add 200 elements in the stack, hence i need to have a reallok function which will give 10 more spaces in memory for new elements each time the position gets more than current size-1

the code for reallok is this

Code:

int *stack::reallok(int *x,int &size){
    
    int *y,i;
    size = size+10;
    y = new int[size];
    for(i=0;i<size-10;i++){
                      y[i] = x[i];
                      }
    delete x;
    return y;  
    
}

i hope it's correct now

it returns the address of the first element of the array that was created in the heap

it has two parameters, *x points is a pointer to the x array of the class, the size is the current size of the stack

then i create a new pointer y and assign size+10 elements for it using new

and then i just copy the values from x to y, then delete x and then return y which is the address of the new memory that was allocated

i hope it's correct now

The code is not correct.
First, I would increase allocation by 2x or 1.5x. Adding 10 each time will hurt performance.
I'd also use std::copy(x, x + size, y) instead of your loop (update size AFTER you copy over the elements).
Finally, you must do delete [] x. If you use new[], then you must use delete [].

And as for the interface:
pop return take no parameters and return the element it pops.
You are missing a peek function which returns the top element.

After that, you need to fix your indentation and also remember not to remove the names of the parameters in your declarations.

A destructor runs when the object is destroyed. There is nothing else to that. Yes, your stack should use a destructor to free its memory when destroyed, but that has nothing to do with the delete statement.
Since you allocate memory with new[], you must free it with delete[]. Simple. What is so difficult in understanding that?

About pop, I mean it should look like this:
int pop();

You are confusing destructors with something. Do you know what they are?
About x or y--it doesn't matter! Whatever you allocate with new [] MUST be freed with delete [], regardless if it's x, y, z, 123 or !"#.
Since you allocate memory with new[] and store it in x, then you must use delete[] on x, as well. Just delete won't work.