#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
#include <string.h>

#define MAXOP 100
#define NUMBER_SIG '0'
#define SPECIAL_SIG '1'
#define VARIABLE_SIG '2'
#define ALPHABET_LEN  26
#define ON 1 
#define OFF 0
#define MAXBUFF 100

char buff[MAXBUFF];
double pop(void);
void push(double f);
char getop(char str[]);
void ptop(void);
void duplitop(void);
void swaptoptwo(void);
void clearstack(void);
void do_special(char str[]);
char getch(void);
void ungetch(char input);
double last_print;

int bp = 0;

int 
main(void)
{
  char str[MAXOP];
  char vars[ALPHABET_LEN];
  char vars_state[ALPHABET_LEN];
  char type;
  double op2;

  for (int i = 0; i < ALPHABET_LEN; i++)
    vars_state[i] = OFF;
  
  vars_state[ALPHABET_LEN-1] = '\0';

  while ((type = getop(str)) != EOF) {
    switch (type) {
      case NUMBER_SIG :
        push(atof(str));
        break;
      case SPECIAL_SIG :
        do_special(str);
        break;
      case VARIABLE_SIG :
        /* Assuming variabke can only be set once */
        if (vars_state[*str-'a'] == 1)
          push(vars[*str-'a']);
        else {
          vars_state[*str-'a'] = ON;
          push(vars[*str - 'a'] = pop());
        }
        break;
      case '+' :
        push(pop() + pop());
        break;
      case '*' :
        push(pop() * pop());
        break;
      case '-' :
        op2 = pop();
        push(pop() - op2);
        break;
      case '/' :
        if ((op2 = pop()) == 0.0)
          printf("Err: deviser cant be zero\n");
        else 
          push(pop() / op2);
        break;
      case '%' :
        op2 = pop();
        if (op2 != 0)
          push(fmod(pop(), op2));
        else 
          printf("Err: deviser cant be zero\n");
        break;
      case '^' :
        ptop();
        break;
      case '>' :
        duplitop();
        break;
      case '#' :
        swaptoptwo();
        break;
      case '<' :
        clearstack();
        break;
      case '\n' :
        printf("%.8g\n", (last_print = pop()));
        break;
      default :
        printf("Err: unknown command\n");
    }
  }

  return 0;
}

#define MAXVAL 100
double val[MAXVAL];
int sp = 0;

void 
do_special(char str[])
{
  double tempop;

  if (!strcmp(str, "sin"))
    push(sin(pop()));
  else if (!strcmp(str, "exp"))
    push(exp(pop()));
  else if (!strcmp(str, "pow")) {
    tempop = pop();
    push(pow(pop(), tempop));
  }
}

void
ptop(void)
{
  if (sp > 0)
    printf("Top of the stack: %.8g\n", (last_print = val[sp-1]));
  else 
    printf("Err: stack is empty\n");
}

void 
duplitop(void)
{
  val[sp] = val[sp-1];
  ++sp;
}

void 
swaptoptwo(void)
{
  double temp1 = pop();
  double temp2 = pop();

  push(temp1);
  push(temp2);
}

void
clearstack(void)
{
  sp = 0;
}

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

void
push(double f)
{
  if (sp < MAXVAL)
    val[sp++] = f;
  else
    printf("Err: stack is full\n");
}

char 
getop(char str[])
{
  char input;
  int i;

  /* ignore blanks */
  while ((input = str[0] = getch()) == ' ' || input == '\t');

  if (isalpha(input)) {
    i = 1;
    while(isalpha(str[i++] = input = getch()));
    str[--i] = '\0';
    ungetch(input);

    /* all single chars are reserved for variables*/
    if (i == 1)
      return VARIABLE_SIG;

    return SPECIAL_SIG;
  }
  
  /* return operator */
  if (!isdigit(input) && input != '.')
    return input;

  /* collect digits*/
  for (i = 1; i < MAXOP && (isdigit(input=getch()) || input == '.'); i++)
    str[i] = input;

  str[i] = '\0';

  if (input != EOF)
    ungetch(input);

  return NUMBER_SIG;
}

char
getch(void)
{
  return (bp > 0) ? buff[--bp] : getchar();
}

void
ungetch(char input)
{
  if (bp < MAXBUFF)
    buff[bp++] = input;
  else {
    printf("Err: buffer full\n");
  }
}