C++ Stack Implementation

Question

Hey all! Having a little trouble with my stack. Im trying to print each element that I've pushed onto the stack.

Starting with the stack ctor we know that we have a fixed size for the array. So I allocate the items struct object to hold just that much space:

stack::stack(int capacity)
{   
  items = new item[capacity];

  if ( items == NULL ) {
    throw "Cannot Allocoate Sufficient Memmory";
    exit(1); 
  }
  maxSize = capacity;
  top       = -1;
}

Yes, items is a struct type of the object "item". Have a look:

class stack
{
  stack(int capacity);
  ~stack(void);
...
  private:
    int maxSize; // is for the item stack
    int top;     // is the top of the stack
    struct item {
      int n;
    };
    item        *items;                 

  public:
    friend ostream& operator<<(ostream& out, stack& q)
  ...

First and formost we want to add to the stack by pushing each incoming element into the array FILO:

bool stack::pushFront( const int n )
{
     if ( top >= maxSize-1 ) 
{
    throw "Stack Full On Push";
    return false;
}
else 
{
    ++top;
    items[top].n = n;
}
return true;
}

// just a textbook example here:
stack::~stack(void)
{
  delete [] items;

  items    = NULL;
  maxSize = 0;
  top      = -1;
}

Yes the real issue for me is the items[++top].n = n; statement. I've been trying to find out how I can drag (+) the items array out to see ALL of the array elements after I push onto the stack.

Im wondering why I cant drag that items[++top].n = n statement out when im debugging. All that comes up is the value that is passed as an 'n' paramater. Do I need to use a stack object type array to store the values into?

When I overload the << operator and try to print the elements I get an insanely large negative number:

ostream& operator<<(ostream& out, stack& q)
{
    if ( q.top <= 0 ) // bad check for empty or full node
    out << endl << "stack: empty" << endl << endl;
    else
        for ( int x = 0; x < q.maxSize; x++ )
        {
            out << q.items[x].n; // try to print elements
        }
    return out;
}

I'm way off and I need some guidence if anyone has the time!

You want to view the items in debugger? Which editor you are using? — Naveen
Don't use the pre tag on SO, but the code indent button instead; see my last edit. — Martin v. Löwis
when im debugging in Visual Studio their is a little plus sign next to that auto varaible items[++top].n I click that but I only get the value that is passed as a paramater. You Know Linked Lists? Where you can drag all those nodes out..thats what I mean lol sorry for the confusion and thanks for the help! — user40120
We all assume you have defined the copy constructor and assignment operator. Otherwise the code is dangerous to use. — Martin York

Naveen Naveen · Accepted Answer · 2009-09-10T05:42:04

In the overloaded << operator in the for loop you are iterating maxsize times. But you might not have pushed maxsize elements into the stack. You should iterate top times. Also, write a default constructor for item structure and initialize all the variblaes so that you do not get garbage values when you try to print them.

C++ Stack Implementation

2 Answers