const int end = 0;
// variebling count parameters: sum
int sum(int beg, ...)
{
   int* pointer = &beg;
   int sum = 0;
   for(; *pointer != end; pointer++)
     sum += *pointer;
return sum;
}

int stack[0x100];
int upper = 0;
const int end = 0;
void push(int arg1, ...)
{
   int* pointer = &arg1;
   for(; *pointer != end; upper++, pointer++)
     stack[upper]     = *pointer;
}

int strlen(char *str)
{
   int count;
   for(count = 0; *str!='\0'; str++, count++) {}
   return count;
}

class stack
{
  public:
     virtual void push(int) = 0;
     virtual int pop() = 0;
   private:
     int *stack_buff;
     int upper;
};

class array_stack : public stack
{
// ......
};
   
class my_stack : public stack
{
//.....
}

void my_func(stack arg) // можем передать и my_stack и array_stack
{
arg.push(12);
//....
}