// C high level skill

#include <stdio.h>

typedef struct {
    int sub;
}sub_t;

typedef struct s_type_int{
    int type;   //int: 0, double: 1, ...
    int i;
    double d;
    sub_t s;

    int (*inc)(struct s_type_int* );
    double (*result)(struct s_type_int* );
}type_int;


double result(type_int *t)
{
    if (t->type == 0) {
        return (int)(t->i - t->s.sub);
    } else if (t->type == 1) {
        return t->d - t->s.sub;
    }
}

int int_inc(type_int *t) // handler function
{
    ++t->i;
    return 0;
}

int double_inc(type_int *t)  // handler function
{
    t->d++;
    return 0;
}

int sub_inc(type_int* t)    // handler function
{
    ++t->s.sub;
    return 0;
}

int main(int argc, char** argv)
{
    type_int a = {0, 0, .0, 0};
    a.result = result;

    a.type = 0;
    a.inc = int_inc;
    a.inc(&a);
    a.inc(&a);
    a.inc(&a);
    a.inc(&a);
    a.inc(&a);
    a.inc(&a);

    a.inc = double_inc;
    a.inc(&a);

    a.inc = sub_inc;
    a.inc(&a);

    printf("%f\n", a.result(&a));
    return 0;
}