在主函数中给类中的字符串类型对象赋值出现问题

//这是类部分：
class Student
{
    private:
        string name;
        char sex;
        int ID;
        int num;
        int score;
    public:
        Student(){name="zero";sex=0;ID=0;num=0;score=0;}
        Student(string na,char s,int i,int n,int sc):name(na),sex(s),ID(i),num(n),score(sc){}
        void change(Teacher &t);
        void display();
        friend Teacher;
};

//这是主函数部分：
Student s1("zhangli","m",46003199209090033,2013011140,88),s2;