【20分】D. 矩阵相乘(运算符重载)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。

好的，我来为您解答。针对您的问题，以下是代码实现：

#include <iostream>
using namespace std;

class MyMatrix {
private:
    int row, col;
    double *data;

public:
    MyMatrix(int r = 0, int c = 0): row(r), col(c) {
        data = new double[row * col];
        for (int i = 0; i < row * col; i++) {
            data[i] = 0;
        }
    }

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

    ~MyMatrix() {
        delete []data;
    }

    MyMatrix &operator=(const MyMatrix &m) {
        if (this == &m) {
            return *this;
        }
        delete []data;
        row = m.row;
        col = m.col;
        data = new double[row * col];
        for (int i = 0; i < row * col; i++) {
            data[i] = m.data[i];
        }
        return *this;
    }

    MyMatrix operator*(const MyMatrix &m) const {
        if (col != m.row) {
            cerr << "Error: matrix size mismatch!" << endl;
            exit(1);
        }
        MyMatrix result(row, m.col);
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < m.col; j++) {
                double sum = 0;
                for (int k = 0; k < col; k++) {
                    sum += data[i * col + k] * m.data[k * m.col + j];
                }
                result.data[i * result.col + j] = sum;
            }
        }
        return result;
    }

    friend istream &operator>>(istream &in, MyMatrix &m) {
        for (int i = 0; i < m.row * m.col; i++) {
            in >> m.data[i];
        }
        return in;
    }

    friend ostream &operator<<(ostream &out, const MyMatrix &m) {
        for (int i = 0; i < m.row; i++) {
            for (int j = 0; j < m.col; j++) {
                out << m.data[i * m.col + j] << " ";
            }
            out << endl;
        }
        return out;
    }
};

int main() {
    int r1, c1, r2, c2;
    cout << "请输入第一个矩阵的行数和列数: ";
    cin >> r1 >> c1;
    MyMatrix m1(r1, c1);
    cout << "请输入第一个矩阵: " << endl;
    cin >> m1;

    cout << "请输入第二个矩阵的行数和列数: ";
    cin >> r2 >> c2;
    MyMatrix m2(r2, c2);
    cout << "请输入第二个矩阵: " << endl;
    cin >> m2;

    MyMatrix result = m1 * m2;
    cout << "矩阵相乘的结果为: " << endl;
    cout << result;

    return 0;
}

运行结果：

请输入第一个矩阵的行数和列数: 2 3
请输入第一个矩阵: 
1 2 3
4 5 6
请输入第二个矩阵的行数和列数: 3 2
请输入第二个矩阵: 
7 8
9 10
11 12
矩阵相乘的结果为: 
58 64 
139 154 

以上代码实现了矩阵类MyMatrix，并对运算符*进行了重载，以实现矩阵相乘的功能。在主函数中，先输入两个矩阵的行列数和元素，然后将它们相乘，输出结果。