Extend the reverse polish calculator.

#include<stdio.h>
#include<math.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 */
int main(){
    int i, type, var =0;

    double   op2, v;
    char     s[MAXOP];
    double   variable[26];

   for(i =0; i < 26;i++)
       variable[i] = 0.0;
   while((type =getop(s)) != EOF){
       switch(type){
           case NUMBER:
                push(atof(s));
                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 '=':
                  pop();
                  if (var >= 'A' && var <= 'Z')
                       variable[var -'A'] = pop();
                  else
                      printf("error: no variable name\n");
                  break;
         case '\n':
              v = pop();
              printf("\t %.8g\n", v);
              break;
         default:
             if (type >='A'  && type <= 'Z')
                  push(variable[type - 'A']);
              else if (type == 'v')
                  push(v);
             else
                 printf("error: unknown command %s\n", s);
             break;
       }
        var = type;
   }
    return 0;
}