-- Assignment : Homework due Sept. 21st, 2006
-- Programmer : Daniel Koestler
-- Course     : CS 240
-- Date       : Sept. 20th, 2006
-- Compiler   : gcc with gnat
-- Professor  : Elizabeth Adams
-- Filename   : stack.adb
-- Executable :
-- Version    : 0.2

-- Purpose: To implement the stack data type as dicussed in class.

-- Input : none

-- Output
--      To Screen    : Messages in the event of an error pushing or
--                     popping from a full or empty stack, respectively.

-- Modifications:
--
--  Version 0.2 :   A typo fixed in the peek declaration!

with ada.text_io;
-- use ada.text_io;


package body stack is

-- pre-Condition : theStack exists  and theValue exists
-- post-Condition : theValue has been added to the stack
-- raises error if theStack is full
   procedure push ( theStack : in out stackType;
                    theValue : in Integer ) is
   begin
      if not (theStack.top = theStack.MAXDATA ) then
  		  theStack.top := theStack.top + 1;
    	  theStack.aStack(theStack.top) := theValue;
      else
        ada.text_io.put_line ( "A number could not be added to the stack, because it is full.");
      end if;
   end push;



   procedure pop ( theStack : in out stackType;
                   theValue : out Integer ) is
   begin
      if ( theStack.top > 0  ) then
         theValue := theStack.aStack(theStack.top);
         theStack.top := theStack.top - 1;
      else
         ada.text_io.put_line ("A number could not be popped off of the stack, because it is empty.");
      end if;
   end pop;

   procedure peek ( theStack : in stackType;
                    theValue : in out Integer ) is
   begin
      if ( theStack.top /= 0 ) then
        theValue := theStack.aStack(theStack.top);
      else
       ada.text_io.put_line ("A number could not be peeked at, because the stack is empty.");
      end if;
   end peek;

   procedure makeEmpty ( theStack : in out stackType ) is
   begin
      theStack.top := 0;
   end makeEmpty;

   function isFull ( theStack : in stackType ) return boolean is

      result : boolean;
   begin
      result := false;

      if ( theStack.top > theStack.MAXDATA ) then
        result := true;
      end if;

      return result;
   end isFull;

   function isEmpty ( theStack : in stackType ) return boolean is

      result : boolean;
   begin
      result := false;

      if ( theStack.top = 0 ) then
         result := true;
      end if;

      return result;

   end isEmpty;


end stack;