Array Implementation of a Stack

In C++, we could implement an array-based stack as a class.

Data members

• stk_array - Stack array pointer. A pointer to the data type of the items stored in the stack; points to the first element of a dynamically-allocated array.
• stk_capacity - Stack capacity. The number of elements in the stack array.
• stk_size - Stack size. The number of items currently stored in the stack. The top item in the stack is always located at subscript stk_size - 1.

Member Functions

The example functions described here correspond to the interface of the stack class in the C++ standard library. Variations are certainly possible.

1. Default constructor

   Sets stack to initial empty state. The stack capacity and stack size should be set to 0. The stack array pointer should be set to nullptr.

2. size()

   Returns the stack size.

3. empty()

   Returns true if the stack size is 0; otherwise, false.

4. clear()

   Sets the stack size back to 0. Does not deallocate any dynamic storage.

5. top()

   Returns the top item of the stack (stk_array[stk_size - 1]).

6. push()

   Inserts a new item at the top of the stack.

   procedure push(value: item to insert)
       // If stack is full, reserve additional storage.
       if stk_size == stk_capacity
           if stk_capacity == 0
               reserve(1)
           else
               reserve(stk_capacity * 2)
           end if
   
       // Insert value into stack array and increment stack size.
       stk_array[stk_size] ← value
       stk_size ← stk_size + 1
   end procedure
   

7. pop()

   Removes the top item from the stack.

   procedure pop()
       stk_size ← stk_size - 1
   end procedure
   

8. Copy constructor

   Similar to the copy constructor for the example Vector class in the notes on dynamic storage allocation.

9. Copy assignment operator

   Similar to the copy assignment operator for the example Vector class in the notes on dynamic storage allocation.

10. Destructor

    Deletes the stack array.

11. reserve()

    Reserves additional storage for the stack array.

    procedure reserve(n: amount of storage to reserve)
        if n < stk_size or n == stk_capacity
            return
        end if
        
        Allocate a new array of size n called temp_array
        
        Copy the contents of stk_array into temp_array
        
        stk_capacity ← n
        
        Delete the stk_array
        
        stk_array ← temp_array
    end procedure