下面代码在 main() 中有一行会导致编译错误，请找出来

class Student{
public:
    Student(string n, int s): name(n), score(s){}
    string getName(){
        return name;
    }
    void setScore(int s){
        score= s;
    }
private:
    string name;
    int score;
};

int main(){
    Student stu("Tom", 85);
    cout<< stu.getName();  // ①
    stu.setScore(90);      // ②
    stu.score= 100;        // ③
    cout<< stu.getName();  // ④
    return 0;
}