#include<stdio.h>
#include<stdlib.h>  // for atof()

#define MAXOP 100 //max size of operand or operator
#define NUMBER '0' // signal that a number wes found

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

//reverse polish calculator
main()
{
  int type;
  double op2;
  char s[MAXOP];

  while((type= getop(s))!=EOF){
    switch(type){
     case NUMBER:
       push(atof(s));
       break;
     case '%':   <-------------------------------------------이부분이 계속 오류나는 이유좀 알려주세요...
       push(pop() % pop());
       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("error: zero dibisor\n");
       break;
     case '\n':
      printf("\t %.8g \n",pop());
       break;
     default:
       printf("error : unknown command %s\n",s);
      break;
     }
   }
   return 0;
}

#define MAXVAL 100 // maximum depth of val stack

int sp = 0; // next free stack position
double val[MAXVAL];

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

// pop : pop and return to p value from stack                                                
double pop(void)
{
  if (sp > 0)
    return val[--sp];
  else{
    printf("error : stack empty \n");
   return 0.0;
  }
}

#include<ctype.h>

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

// getop : get next operator or numeric operand
int getop(char s[])
{
  int i,c;

  while((s[0] = c = getch()) == ' ' || c == '\t')
   ;
  s[1] = '\0';
  if(!isdigit(c) && c != '.')
    return c; //not a number
  i=0;
  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;
}

#define BUFSIZE 100

char buf[BUFSIZE]; // buffer for ungetch
int bufp = 0;  // next free position int 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
{
  if(bufp >= BUFSIZE)
    printf("ungetch: too many charcater \n");
 else
   buf[bufp++]=c;
}