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


const int ERR_NS_OPERANDS       = 1;
const int ERR_NS_OPERATORS      = 2;
const int ERR_INVALID_INPUT     = 4;
const int ERR_INVALID_FACTORIAL = 8;


struct EE_STACK_NODE {
    double datum;
    struct EE_STACK_NODE* tail;
};
typedef struct EE_STACK_NODE NODE;
typedef struct EE_STACK_NODE* STACK;

STACK   push(double,STACK);
STACK   pop(STACK);
double  peek(STACK);

int     isNum(const char*);
int     arrity(const char);

double  evaluate(STACK*, char);
double* operands(STACK*, int);
double  fact(int n);

void    report();