#include<iostream>using namespace std;int sum(int x,int y){return x+y}int product(int x,int y){return x*y}void main(){?————————（填一些）?int a, b, result;?cout << "a="; cin >> a;?cout << "b="; cin >> b;?pf = sum; result = pf(a, b);?cout << a << "+" << b << "=" << result << endl;?pf = product; result = pf(a, b);?cout << a << "*" << b << "=" << result << endl;}不懂 這里的調用