C++ stack using class

hi guys, im trying to figure out why my program is not working, it's not finished yet, but i cant understand why its not working until now

Code:

//stack with integers

#include <iostream>

using namespace std;

      
      
class stack{
      int pos;
      int *a;
      int check;
      public:
             stack();
             void freestack();
             void add(int);
                  
      };
      
stack::stack(){

                     check = 1;
                     a = new int[10];
                     cout<<"array of 10 has been created..."<<endl;
                     pos = 0;

                     }

void stack::freestack(){

                        delete[] a;

                        }
void stack::add(int n){

               if (pos<check*10){

                  *(a+pos) = n;
                  pos++;
                  cout<<"New integer added"<<endl;

                  }

               else {

                       a = (int *)realloc(a,++check*10*sizeof(int)); // idont know how to do this in c++

                       if (a!=NULL){
                                    cout<<"More memory assigned\n"<<endl;
                                    pos++;
                                    a[pos]=n;
                                    cout<<"New integer added"<<endl;
                                    }

                       }

         }
int main(void){
    
    stack newstack;
    newstack.freestack();
    newstack.add(1);
    system("pause");
    
    
    return 0;
}

i think that the problem is in this line

Code:

a[pos] = n;

because when i comment this line then the program works fine, i cant understand why its not working there

I mean I have the pos variable which is private, so is the array, i have allocated 40 bytes in the constructor and the a variable points to the first element of the allocated memory in heap

but why doesnt this work?

thanks in advance

It looks like you never actually initialise pos to anything. By the way, you really need to indent your code properly.

doesnt it get initialized in the constructor?

Edit: sorry for the code i made it very quickly

Originally Posted by nik2

doesnt it get initialized in the constructor?

Oh, no it does not, since you failed to use the constructor initialisation list. But it does get assigned to in the constructor, so that is probably not the problem. The next problem might lie with how you are expanding the dynamic array: you increment pos prematurely.

Oh, and speaking of that, I suggest that you avoid the use of malloc, realloc and free here. You may want to extend this exercise to objects of class types, upon which the use of these functions in this way would be incorrect. Use new[] and delete[] instead. Actually, it would be even easier to use a std::deque<int> like std::stack so as to concentrate on getting the stack operations right instead of also dealing with dynamic memory allocation at the same time.

Before making any further replies, fix your indentation. Now.

i edited the code but im not sure if thats what you mean when you say "indentation"

after i changed the malloc and free the result is the same i get the same problem

ok i think i have it correct right now


i made 3 different files, main.cpp has the main function, stack.h has the class and functions.cpp has the class functions

im not sure about the realloc though, i dont know if there is a function for this, but i made one that does a similar job
sorry for replying so late, i forgot this problem

Edit: oh, i should have made the reallok function private

Google isn't an option for you? Indent style - Wikipedia, the free encyclopedia
Again, forget about realloc. Use a vector. Realloc should not, must not be used with new and delete.

You can use realloc if you want, just don't use it on variables initialized with new (only with malloc) and use free() on them, not delete.

Don't use realloc in C++ at all. Use new and delete.
But you don't even need them here. They're tricky and should be avoided.

Originally Posted by Elysia

Google isn't an option for you? Indent style - Wikipedia, the free encyclopedia
Again, forget about realloc. Use a vector. Realloc should not, must not be used with new and delete.

actually thats the first thing i saw about indentation, i hope i have it correct in the files

Edit: about the realloc, yea when i used it it didnt work at all, im new to C++ i dont know anything about vectors yet, that's why i created a reallok that does a similar job with realloc

i ll definitely search for vectors later on, thanks for your help guys

Originally Posted by Elysia

Don't use realloc in C++ at all.

You can if you want Not to say that is wise or recommended, just that there is nothing strictly "wrong" about it other than (some people's ideas about) style.

Calling new and delete tricky is like calling shoe tying dangerous. Remember to use a bow and make sure the ends do not touch the ground and you'll be fine.

We're talking about a newbie here. I would not recommend new and delete to a newbie. Dangerous stuff. Easy to shoot yourself in the foot. So easy to create bugs. Use already proven working solutions if you can!
And while realloc is not Evil™, do not recommend it to a newbie. There are areas where it might be needed, but never for pure C++ and especially not for a learner of the language. Dangerous things.

You can if you want Not to say that is wise or recommended, just that there is nothing strictly "wrong" about it other than (some people's ideas about) style.

Well it can be wrong. Particularly when you mix C's flavor of this with C++. new and delete do not have to be implemented in terms of malloc and free, (and AFAIK aren't) so if you just realloc something from new somewhere, you might end up with two different allocations, or worse.

pushing and popping at an index does not a stack make.

what the heck is freestack() and reallok()?

Here are the signatures of the functions you need to implement:

Code:

Stack();    // should initialize a pointer, and the value of size
~Stack();    // pops until empty

void push(int);    // adds *something* to the top, move pointers around

void pop();    // takes no argument, removes the top, move pointers around

int top();    // returns the int at the top of the stack

int size();    // returns the value of size

bool empty();    // returns true of false (hint: use size)

EDIT: Here's a few more hints to save time:

The private members stack needs:

Code:

Node* top;
int size;

// ... And a node struct...

struct
{
    int data;
    Node* next;
};

I leave the rest to you

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.