矩阵相乘（运算符重载）

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1.题目概述

定义一个矩阵类MyMatrix，并且在类中进行运算符重定义，用*实现矩阵相乘。要求必须对运算符进行重载，如果用函数如multiply（matrix，matrix）去实现矩阵之间的运算一律记0分。

必须包含以下析构函数，其中n是矩阵的阶数，data是存放矩阵数据的二维动态数组：

MyMatrix::~MyMatrix() { // 释放空间 for (int i = 0; i < n; i++) { delete[] data[i]; } delete[] data; }

矩阵相乘的具体内容不在此赘述

2.代码

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#include <iostream>
using namespace std;

class MyMatrix
{
private:
    int** data;
    int my_n;
public:
    MyMatrix()
    {
        my_n = 100;
        data = new int* [100];
        for (int i = 0; i < 100; i++)
        {
            data[i] = new int[100];
        }
    }
    MyMatrix(int n, int** t)
    {
        my_n = n;
        data = new int* [n];
        for (int i = 0; i < n; i++)
        {
            data[i] = new int[n];
        }

        for (int i = 0; i < n; i++)
        {
            for (int j = 0; j < n; j++)
            {
                data[i][j] = t[i][j];
            }
        }
    }

    MyMatrix(const MyMatrix& m)
    {   
        my_n = m.my_n;
        data = new int* [m.my_n];
        for (int i = 0; i < m.my_n; i++)
        {
            data[i] = new int[m.my_n];
        }

        for (int i = 0; i < my_n; i++)
        {
            for (int j = 0; j < my_n; j++)
            {
                data[i][j] = m.data[i][j];
            }
        }

    }

    MyMatrix operator*(MyMatrix m)
    {
        int** arr = new int* [my_n];
        for (int i = 0; i < my_n; i++)
        {
            arr[i] = new int[my_n];
        }

        for (int i = 0; i < my_n; i++)
        {
            for (int j = 0; j < my_n; j++)
            {
                int num = 0;
                for (int k = 0; k < my_n; k++)
                {
                    num += data[i][k] * m.data[k][j];
                }
                arr[i][j] = num;
            }
        }

        MyMatrix res(my_n, arr);

        for (int i = 0; i < my_n; i++)
        {
            delete[] arr[i];
        }
        delete[] arr;

        return res;
    }

    MyMatrix& operator=(const MyMatrix& m) {
        if (this == &m) return *this; 

        for (int i = 0; i < my_n; i++) {
            delete[] data[i];
        }
        delete[] data;

        my_n = m.my_n;
        data = new int* [my_n];
        for (int i = 0; i < my_n; i++) {
            data[i] = new int[my_n];
            for (int j = 0; j < my_n; j++) {
                data[i][j] = m.data[i][j];
            }
        }

        return *this; 
    }

    ~MyMatrix() {
        for (int i = 0; i < my_n; i++)
        {
            delete[] data[i];
        }
        delete[] data;
    }

    void print()
    {
        for (int i = 0; i < my_n; i++)
        {
            cout << data[i][0];
            for (int j = 1; j < my_n; j++)
            {
                cout<< " " << data[i][j] ;
            }

            if (i != my_n - 1) cout << endl;
        }
    }
};


int main()
{
    int c;
    int n;
    cin >> c >> n;

    int** arr = new int* [n];
    for (int i = 0; i < n; i++)
    {
        arr[i] = new int[n];
    }

    MyMatrix** m = new MyMatrix*[c];



    for (int i = 0; i < c; i++)
    {
        for (int j = 0; j < n; j++)
        {
            for (int k = 0; k < n; k++)
            {
                cin >> arr[j][k];
            }
        }
        m[i] = new MyMatrix(n, arr);
    }

    MyMatrix res = *(m[0]);
    for (int i = 1; i < c; i++) {
        res = res * (*m[i]);
    }

    res.print();

    for (int i = 0; i < n; i++)
    {
        delete[] arr[i];
    }
    delete[] arr;

    for (int i = 0; i < c; i++) {
        delete m[i];
    }
    delete[] m;

    return 0;
}

重点：

1.主函数中，构造res时会调用拷贝构造函数，由于MyMatrix类中数据涉及到指针，所以要写深拷贝。

2.在做乘法时，res * (*m[i])会返回一个临时对象，这个对象将对res重新赋值，所以设计到赋值运算符的重载。