(1)有两个矩阵a和b，均为2行3列。求两个矩阵之和。重载运算符“+”，使之能用于矩阵相加。如: c=a+b。 (2)编写一个友元函数来读取矩阵指定所在行列的值。 。(3)定义一个Teacher(教师)类和一个Student(学生)类，二者有一部分数据成员是相同的，例如num(号码)，name(姓名),sex(性别)。编写程序，将一个Student对象(学生)转换为Teacher(教师)类，只将以上3个相同的数据成员移植过去。可以设想为:一位学生大学毕业了，留校担任教师，他原有的部分数据对现在的教师身份来说仍然是有用的，应当保留并成为其教师的数据的一部分。

(1) 代码如下：

#include<iostream>
using namespace std;

class Matrix {
private:
    int m[2][3];
public:
    Matrix(int a[2][3]) {
        for (int i = 0; i < 2; i++)
            for (int j = 0; j < 3; j++)
                m[i][j] = a[i][j];
    }
    Matrix operator+(const Matrix& n) const {
        Matrix sum({0});
        for (int i = 0; i < 2; i++)
            for (int j = 0; j < 3; j++)
                sum.m[i][j] = m[i][j] + n.m[i][j];
        return sum;
    }
    friend int getElement(Matrix& n, int i, int j);
};

int getElement(Matrix& n, int i, int j) {
    return n.m[i][j];
}

int main() {
    int a[2][3] = { {1,2,3},{4,5,6} };
    int b[2][3] = { {7,8,9},{10,11,12} };
    Matrix m1(a), m2(b), m3({0});
    m3 = m1 + m2;
    cout << "The sum of two matrices is: " << endl;
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++)
            cout << m3.getElement(m3, i, j) << " ";
        cout << endl;
    }
    return 0;
}

(2) 友元函数的代码如下：

#include<iostream>
using namespace std;

class Matrix {
private:
    int m[2][3];
public:
    Matrix(int a[2][3]) {
        for (int i = 0; i < 2; i++)
            for (int j = 0; j < 3; j++)
                m[i][j] = a[i][j];
    }
    Matrix operator+(const Matrix& n) const {
        Matrix sum({0});
        for (int i = 0; i < 2; i++)
            for (int j = 0; j < 3; j++)
                sum.m[i][j] = m[i][j] + n.m[i][j];
        return sum;
    }
    friend int getElement(Matrix& n, int i, int j);
};

int getElement(Matrix& n, int i, int j) {
    return n.m[i][j];
}

int main() {
    int a[2][3] = { {1,2,3},{4,5,6} };
    Matrix m1(a);
    cout << "The element of matrix at row 1, column 2 is: " << getElement(m1, 1, 2) << endl;
    return 0;
}

(3) 学生转教师的代码如下：

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

class Student {
protected:
    int num;
    string name;
    string sex;
public:
    Student(int n, string na, string s) :num(n), name(na), sex(s) {}
    void display() {
        cout << "The information of student is: " << endl;
        cout << num << " " << name << " " << sex << endl;
    }
};

class Teacher :public Student {
private:
    string course;
public:
    Teacher(Student s, string c) :Student(s.num, s.name, s.sex), course(c) {}
    void display() {
        cout << "The information of teacher is: " << endl;
        cout << num << " " << name << " " << sex << " " << course << endl;
    }
};

int main() {
    Student s(1001, "Tom", "Male");
    Teacher t(s, "Math");
    t.display();
    return 0;
}