Reverse polish calculator

#include <stdio.h>
#include <stdlib.h>   /* for atof */

#define MAXOP  100    /*max size of operand or operator */
#define NUMBER '0'    /*signal that a number was found */

int getop(char []);
void push(double);
double pop(void);

/*reverse Polish calculator */
main(){
     int type;
     double op2;
     char s[MAXOP];

     while ((type =getop(s)) != EOF){
           switch(type){
           case NUMBER:
               push(atof(s));
               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)
                  push(pop() / op2);
               else
                   printf("error: zero divisor\n");
               break;
          case '\n':
               printf("\t%.8g\n",pop());
               break;
          default:
               printf("error: unknown command %s\n", s);
               break;
           }
     }
     return 0;
}