// rpn.c: reverse polish notation calculator

#include "stack.h"
#include <stdio.h>
#include <stdlib.h>

#define MAXOPSIZE       20      /* maximum size of operand, operator */
#define NUMBER          '0'     /* indicates number found */
#define TOOBIG          '9'     /* indicates string is too big */

int getop(char *dest, int limit);

int main() {
   int  type;
   char input[MAXOPSIZE];
   double op2;

   while ( (type = getop(input, MAXOPSIZE)) != EOF ) {
      switch ( type ) {
      case NUMBER:
         push(atof(input));
         break;
      case '+':
         push(pop() + pop());
         break;
      case '*':
         push(pop() * pop());
         break;
      case '-':
         op2 = pop();
         push(pop() - op2);
         break;
      case '/':
         op2 = pop();
         if ( op2 == 0.0 )
            printf("Divide by zero.\n");
         else
            push(pop() / op2);
         break;
      case '=':
         printf("Top: %f\n", push(pop()));
         break;
      case 'c':
         clear_stack();
         break;
      case TOOBIG:
         printf("Input too large: '%s'\n", input);
         break;
      default:
         printf("Unknown command: '%c'\n", type);
      }
   } // end while
}

int getop(dest, limit)
char *dest;                     // alternative way to specify argument types
int limit;
{
   int i, c;

   while ( (c = getchar()) == ' ' || c == '\t' || c == '\n' )
      ;
   if ( c != '.' && (c < '0' || c > '9') )
      return c;
   dest[0] = c;
   for(i = 1; (c = getchar()) >= '0' && c <= '9'; ++i)
      if ( i < limit )
         dest[i] = c;
   if ( c == '.' ) { // collect fractional portion
      if ( i < limit )
         dest[i] = c;
      for(i++; (c = getchar()) >= '0' && c <= '9'; ++i)
         if ( i < limit )
            dest[i] = c;
   }
   if ( i < limit ) { /* number is ok */
      ungetc(c, stdin);
      dest[i] = '\0';
      return NUMBER;
   } else { /* input is too big; skip rest of line */
      while ( c != '\n' && c != EOF )
         c = getchar();
      dest[limit - 1] = '\0';
      return TOOBIG;
   }
}