#include <stdio.h>
#include <stdlib.h> /* for atof() */
#include <ctype.h>
#include <math.h>
#define MAXOP 100 /* max size of operand or operator */
#define NUMBER '0' /* signal that a number was found */
#define MAXVAL 100 /* maximum depth of val stack */
#define BUFSIZE 100
int sp = 0; /* next free stack position */
double val[MAXVAL]; /* value stack */
int getop(char []);
void push(double);
double pop(void);
/* reverse Polish calculator */
int main(void)
{
    int type;
    int i=0,count=0;
    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(fmod(pop(),op2));
                else
                    printf("error: zero divisor\n");
                    break;
            case '%':
                op2 = pop();
                    if(op2!=0)
                        fmod(pop(), op2);
            case '\n':
                printf("\tanswer is%.8g\n", pop());
                break;
            default:
                printf("error: unknown command %s\n", s);
                break;
        }
    }
    return 0;
}
/* push: push f onto value stack */
void push(double f)
{
 
    if (sp < MAXVAL) {
        val[sp++] = f;
        printf("val[sp]=%g",val[sp]);//we gonna use for verifacation
        getchar();
    }
    else
        printf("error: stack full, can't push %g\n", f);
}
/* pop: pop and return top value from stack */
double pop(void) {
 
    if (sp > 0)
        return val[--sp];
    else {
        printf("error: stack empty\n");
        return 0.0;
    }
}
 
int getch(void);
void ungetch(int);
/* getop: get next character or numeric operand */
int getop(char s[])
{
    int i, c,next;
    while ( (s[0] = c = getch() ) == ' ' || c == '\t');
        s[1] = '\0';
    if (!isdigit(c) && c != '.' && c!='-')
        return c; /* not a number */
    i = 0;
    if(c=='-') {
        //save the variable after it
        next=getch();//get next character
        if(isspace(next))//then its operand
            return c;
        //we didnt do else coz it will be the same since return will return from the whole function
        s[i]=c;//reassign c to negative
        c=next;//assign c to next which is a number after the -
        s[++i]=c;//now assign next character in the array now to the number
    }
    if (isdigit(c)) { /* collect integer part */
        while (isdigit(s[++i] = c = getch()));
    }
    if (c == '.') /* collect fraction part */
        while (isdigit(s[++i] = c = getch()));
    s[i] = '\0';
    if (c != EOF)
        ungetch(c);
    return NUMBER;
}
 
 
char buf[BUFSIZE]; /* buffer for ungetch */
int bufp = 0; /* next free position in buf */
int getch(void) {/* get a (possibly pushed-back) character */
    return (bufp > 0) ? buf[--bufp] : getchar() ;
}
void ungetch(int c) /* push character back on input */
{
    bufp >= BUFSIZE ? printf("ungetch: too many characters\n") : buf[bufp++] = c ;
}