[Dev-C++] reverse polish notation

[chromatonus 7. <chr...@ho...>]

hi, my stack works, (thanks to Mr. Hardman,) but i am now trying to create a 
calculator:  type in digits 0~9 in one line, like this: 123, for example. 
Then if you type in '+', then the prgm pushes the top two # out of stack, 
add them, and pop it back in. So 2 and 3 would be added and 5 is popped in 
on top of 1. same for '*' and '-'. if '=' is typed then the top element of 
the stack is displayed on the screen (like the answer).

i have to make sure that all the input chars be on one line but not 
overlapping, and that my add, subtract and mult. functions work (they 
don't.)

notes: 'q' quits the program and 'i' clears everything on the screen except 
the > prompt.

thank you for your help : )

#include <iostream.h>
#include <conio.h>
#include <stdlib.h>

int const max_stack = 100;

class stacktype
  {
    public:
  		 stacktype();
         	//	default constructor
         	//	postcondition:	initializes stack by setting TOP = 0
         void initialize();
         	//	postcondition:	erase stack by setting TOP = 0
         void push( int );
         	//	postcondition:	If the stack is not full,
            //							increase TOP by 1 , then
            //							put info into DATA[TOP]
         int pop();
         	//	postcondition:	If the stack is not empty,
           	//                 	put DATA[TOP] into x,
            //							decrease TOP by 1,
            //							return x
        	bool is_empty();
         	//	postcondition:	Return true if stack is empty, false otherwise.
         bool is_full();
         	//	postcondition:	Return true if stack is full, false otherwise.
    private:
    		int mydata[max_stack];
         int mytop;			//	subscript of the top of the stack
  };


//==============================================================================
//============================== Free functions 
================================
//==============================================================================

void a_two( stacktype );
   // precondition:  send in stack
   // postcondition: new stack formed with top element = sum of top 2 
elements
   //                of old stack

void s_two( stacktype );
   // precondition:  send in stack
   // postcondition: new stack formed with top element = difference of top 2
   //                elements of old stack

void m_two( stacktype );
   // precondition:
   // postcondition:

void display_top( stacktype );
	//	precondition:	send in stack
   //	postcondition:	display, without destruction, the value in data[top]

//==============================================================================
//============================== Implementation 
================================
//==============================================================================

stacktype::stacktype()
{
   mytop = 0;
}
void stacktype::initialize()
{
   mytop = 0;
   clrscr();
   gotoxy(3,3);
   cout<< "> ";
}
bool stacktype::is_empty()
{
   return (mytop == 0);
}
bool stacktype::is_full()
{
   return (mytop == max_stack-1);
}
void stacktype::push( int x )
{
	if( !is_full() )
   {
      mytop++;
      mydata[mytop] = x;
   }
}
int stacktype::pop()
{
   if( !is_empty() )
   {
      int x = mydata[mytop];
      mytop--;
      return x;
   }
}


//==============================================================================
//============================== Client Program 
================================
//==============================================================================

int main()
{
   int c = 3;
   stacktype S;
   char z;
   gotoxy(3,3);
   cout<< "> ";
   c = 5;
   while( z != 'Q' && z != 'q' )
   {
      gotoxy(c,3);
      cin>> z;
      switch( z )
      {
         case 'I':
         case 'i':  S.initialize();
                    break;

         case '+':  a_two(S);

                    break;

         case '-':  s_two(S);

                    break;

         case '*':  m_two(S);

                    break;

         case '=':  display_top(S);

                    break;

         case '0':
         case '1':
         case '2':
         case '3':
         case '4':
         case '5':
         case '6':
         case '7':
         case '8':
         case '9':  z = getche();
                    int j = z;
                    S.push( j );
                    break;

      }
      c++;
      z = getche();
   }
}

void a_two( stacktype S )
{
   int p = S.pop();
   int q = S.pop();
   S.push( p+q );
}

void s_two( stacktype S )
{
   int p = S.pop();
   int q = S.pop();
   S.push( p-q );
}

void m_two( stacktype S )
{
   int p = S.pop();
   int q = S.pop();
   S.push( p*q );
}

void display_top( stacktype S )
{
   int t = S.pop();
   cout<< t;
   S.push(t);
}








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