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

#define MAXOP 100
#define NUMBER '0'

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

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 '*':
                push(pop() * pop());
                break;
            case '-':
                op2 = pop();
                push(pop() - op2);
                break;
            case '/':
                op2 = pop();
                if(op2 != 0.0)
                    push(pop() / op2);
                else
                    printf("errore: divisione per zero\n");
                break;
            case '\n':
                printf("\t%.8g\n",pop());
                break;
            default:
                printf("errore: comando ignoto %s\n",s);
                break;
        }
    }
    return 0;
}

#define MAXVAL 100

int sp = 0;
double val[MAXVAL];

void push(double f)
{
    if(sp < MAXVAL)
        val[sp++] = f;
    else
        printf("errore; la pila e' piena, non si puo' inserire %g\n",f);
}

double pop(void)
{
    if(sp > 0)
        return val[--sp];
    else
    {
        printf("errore: la pila e' vuota\n");
        return 0.0;
    }
}

#include <ctype.h>

int getch(void);
void ungetch(int);

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

    while((s[0] = c = getch()) == ' ' || c == '\t')
        ;
    s[1] = '\0';

    i = 0;

    if(!isdigit(c) && c != '.')
            return c;

    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;
}

#define BUFSIZE 100

char buf[BUFSIZE];
int bufp = 0;

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

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