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/*	$Id$	*/
/*	Berlin 26.12.2000	*/
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#define MAXOP 100
#define NUMBER '0'
#define MAXVAL 100
#define BUFSIZE 100

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

int sp = 0;
double val[MAXVAL];
int getch(void);
void ungetch(int);
char buf[BUFSIZE];
int bufp = 0;

int main(void) {
    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("Fehler: Teilung durch Null\n");
               break;
          case '\n':
               printf("\t%.8g\n", pop());
               break;
          default:
               printf("Fehler: Unbekanter Befehl %s\n", s);
               break;
          }
    }
    return 0;
}

void push(double f) {
    if (sp < MAXVAL)
        val[sp++] = f;
    else
        printf("Fehler: Stack ist voll, %g passt nicht rein\n", f);
}

double pop(void) {
    if (sp > 0)
        return val[--sp];
    else {
        printf("Fehler: Stack ist leer\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: Zu viele Zeichen\n");
    else
        buf[bufp++] = c;
}