Question

My first ever question here. Please excuse me, I have just entered into C++ and was starting up with DS. STACK!!!

My code: I think

    using namespace std;
    typedef char stackElement;

    class Stack
    {
    public:
        stackElement *contents;   //dynamically allocated: as we do not know what would be the size of our array.
        int top, maxSize;               // current Top index in the array

                //max size of the array; we need it to know if the array is full

    Stack(int maxSize)
    {

        contents = new stackElement(maxSize);
        this.maxSize = maxSize;
        if(contents == NULL)
        {
            cout<<"Insufficient memory";
            exit(1);

        }

        top = -1;
    }
    ~Stack()
    {
        delete [] contents;
        contents = NULL;
        maxSize = 0;
        top = -1;

    }

    bool isEmpty()const
    {

        return top < 0;
    }
    bool isFull() const
    {

        return top == maxSize - 1;
    }


    void push(stackElement element)
    {
        if(isFull())
        {
            cout<<"STACK IS ALREADY FULL";
            exit(1);
        }
        top = top + 1;
        contents[top] = element;
    }


};

int main()
{

    cout<<"STACK IMPLEMENTATION";
    int i = 1;
    Stack s1(i);


    s1.push('a');
    s1.push('1');
    return 0;
}

I am getting this error:

error: request for member 'maxSize' in 'this', which is of non-class type 'Stack* const'

Answer 1

If at all, you’d have to write this->maxSize = maxSize;, since this is a pointer.

But better not to write that at all and instead use the constructor-initializer list:

  explicit Stack(int m)
  : contents(new stackElement[m]), top(-1), maxSize(m)
  {
      // nothing else to do
  }

I also added explicit so you don’t accidentally convert 5 into a Stack.

You also wrote the array initialization wrong.

Also, you don’t need to check that contents is not null: When new fails, it exits with an exception, it does not return a null pointer. (That behaviour would make no sense when you think in terms of objects.)

It is crucial to note that you have at most one naked new-expression in your constructor. Anything else is an exception-safety disaster, and a sign that you need to refactor and use single-responsibility resource-managing classes.

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The destructor should just be: ~Stack() { delete [] contents; } Everything else is pointless waste.

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Imagine you had to pay for every line of code you write. Be patient, lose the source, think.