unit cStack;

  { cStack                                                                         }
  { Copyright © 1992 by Michael J. Gibbs, all rights reserved.                     }
  {                                                                                }
  { This unit provides classes that manage a stack of objects.                     }
  {                                                                                }
  { iStack         - Initializes a new stack object to empty and allocates a list  }
  {                  object to contain the associated data.                        }
  { push           - Adds 'anObject' to the top of the stack object.               }
  { pop            - Returns the object at the top of the stack as the function    }
  {                  result and removes the object from the stack.                 }
  { tos            - Returns the object at the top of the stack as the function    }
  {                  result without removing it from the stack.                    }
  { getNumElements - Returns the number of objects in the stack as the function    }
  {                  result.                                                       }
  { free           - Releases the stack object.  NOTE--this does not release the   }
  {                  individual objects that are contained in the stack, if any.   }

interface

	uses
		objIntf, listObjs;

	type
		cStack = object(tObject)
				itsStackList: cList;
				procedure iStack;
				procedure push (anObject: tObject);
				function pop: tObject;
				function tos: tObject;
				function getNumElements: integer;
				procedure free;
				override;
			end;

implementation

	procedure cStack.iStack;

  { Initialize the stack }

	begin
		new(itsStackList);
		itsStackList.iList;
	end; { cStack.iStack }

	procedure cStack.push (anObject: tObject);

  { Push an object onto the stack }

	begin
		itsStackList.prependToList(anObject);
	end; { cStack.push }

	function cStack.pop: tObject;

  { Pop an object off the stack }

	begin
		pop := itsStackList.getElement(1);
		itsStackList.deleteElement(1);
	end; { cStack.pop }

	function cStack.tos: tObject;

  { Return the object on the top of the stack without popping it }

	begin
		tos := itsStackList.getElement(1);
	end; { cStack.tos }

	function cStack.getNumElements: integer;

  { Return the size of the stack }

	begin
		getNumElements := itsStackList.getNumElements;
	end; { cStack.getNumElements }

	procedure cStack.free;

  { Free the stack }

	begin
		itsStackList.free;
		inherited free;
	end; { cStack.free }

end.