请问为什么会引发这个错误？(语言-c++|开发工具-visualstudio)

Question

#include<iostream>
#include<string>
using namespace std;
struct student
{
    string sname;
    int score;
};
struct teacher
{
    string Tname;
    student stu[5];
};
void fuzhi(teacher T[],int len)
{
    string nameadd = "ABCDE";
    for (int i = 0; i < 3; i++)
    {
        T[i].Tname = "Teacher-";
        T[i].Tname += nameadd[i];
    
    }
    for (int j = 0; j < 5; j++)
    {
        T[j].stu[j].sname = "Student-";
        T[j].stu[j].sname = T[j].stu[j].sname + nameadd[j];
        T[j].stu[j].score = 60;
    }
}
void print(teacher T[],int len)
{
    for (int i = 0; i < len; i++)
    {
        cout << "老师的名字：  "<<T[i].Tname << endl;
        for (int j=0;j<5;j++)
        {
            cout << "学生姓名:  " << T[j].stu[j].sname << 
                "考试得分：  "<<T[j].stu[j].score<<endl;
        }
    }

}
int main()
{
    teacher T[3];
    int len = sizeof(T) /sizeof( T[0]);
    
    fuzhi(T,len);
    print(T,len);

}