设计一个老师类teacher，描述老师的信息（姓名，年龄）和职责（学习）再用继承设计一个·学生的一个类Student，描述学生的信息（姓名，学号）和职责（学习），研究生的类，描述研究生的信息（姓名，年龄，学号）和职责（学习，教学）用继承方法，C++

++代码如下：

#include <iostream>
#include <string>
using namespace std;

class Teacher {
protected:
string name;
int age;
public:
Teacher(string n, int a) {
name = n;
age = a;
}
void teach() {
cout << name << " is teaching." << endl;
}
};

class Student : public Teacher {
private:
string stuNum;
public:
Student(string n, int a, string num) : Teacher(n, a) {
stuNum = num;
}
void study() {
cout << name << " is studying." << endl;
}
};

class Graduate : public Student {
public:
Graduate(string n, int a, string num) : Student(n, a, num) {}
void teach() {
cout << name << " is teaching." << endl;
}
};

int main() {
Teacher t("Mr. Li", 35);
t.teach();

Student s("Tom", 18, "1001");
s.teach();
s.study();

Graduate g("Amy", 25, "2001");
g.teach();
g.study();

return 0;
}