#define MAXINPUT        6                         /* max numbers as input */
#define ALLOCSIZE       1024                      /* # of elements to alloc when needed */
#define EMPTY           -1

typedef enum {
    Nop='N',
    Add='+',
    Sub='-',
    Mul='x',
    Div='/',
    End='\0'                                      /* Only for "printf" */
} OPER;

typedef struct stackelt {
    int val;
    int nop;                                      /* number of operators */
    int curop;                                    /* current operator */
    char op[MAXINPUT];                            /* MAXINPUT-1 + ending \0 */
    int next, prev;                               /* for eval: avoids restructuring stack */
} STACKELT;

typedef struct stack {
    char name[80];
    int size;
    int last;
    int eval;
    STACKELT *stack;
} STACK;

/* tree.c */
extern void gen_tree(int *seq, int n, int nb1, int nb0);

/* stack.c */
extern void print_stack(STACK *stack, int details);
extern STACK *new_stack(int size, char *name);
extern STACKELT *push_stack(STACK *stack, OPER op, int val);
extern STACKELT *pop_stack(STACK *stack);
extern STACK *dup_stack(STACK *stack, char *name);
extern void swap_stack(STACKELT *elts, int i, int j);
extern int permute_stack(STACKELT *array, int n);
extern void mergesort_stack(STACKELT *array, int left, int right);
extern STACKELT *set_op_stack(STACK *stack, int pos, OPER op);
extern STACKELT *set_ops_stack(STACK *stack, char *ops);

/* oper.c */
extern unsigned ncombinations(int nops, int len);
extern char *combination(char *ops, int len, int n);

/* eval.c */
extern int eval_cell(STACKELT *pos);
extern int eval_stack(STACK *stack);