下列 C++程式執行後螢幕呈現的結果為何？ class fraction { private: int num; int den; public: fraction(int x=0, int y=1) { num = x; den = y; } fraction operator ++() { num += den; return *this; } fraction operator +(int i) { num =2*(num+ i*den); den += den; return *this; } void print() { printf("%d/%d\n", num, den);} }; int main(){ fraction BB(2, 3); fraction CC(1, 2); CC = ++BB + 2; CC.print(); return 0; }