/*reverse Polish calculator */
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>

#define  MAXOP 100
#define  NUMBER   '0'
#define  MAXVAL   100
#define  BUFSIZE  100

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

int sp = 0;
double val[MAXVAL];
char buf[BUFSIZE];
int bufp=0;

int 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 '-':     op2=pop();  push(pop() - op2); break;
       case '*':     push(pop() * pop()); 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;
}

void push(double f)
 {
    if(sp < MAXVAL)  val[sp++] = f;
    else
     printf("Error: stack full, can't push %g\n", f);
}

double pop(void)
{
  if(sp > 0)
    return val[--sp];
  else
    {
       printf("Error: stack empty\n");
       return 0.0;
    }
}


int getop(char s[])
{
  int i, c;

    while((s[0] = c = getch()) == ' ' || c == '\t') ;

    s[1] = '\0';
    if(!isdigit(c) && c!= '.') return c;
    i=0;
    if(isdigit(c))
        while(isdigit(s[++i] = c= getch())) ;
    if ( c=='.')
        while(isdigit(s[++i] = c = getch())) ;
    s[i] = '\0';
    if ( c!= EOF) ungetch(c);
    return NUMBER;
}

int getch(void)
 {
    return (bufp > 0) ? buf[--bufp] : getchar();
 }

void ungetch(int c)
 {
   if (bufp >= BUFSIZE) printf("ungetch: too many characters\n");
   else
     buf[bufp++]=c;
}