第10课：二维数组（生成与变换）

1、上下（垂直）翻转规律：行下标反转
    for (int i = n; i >= 1; i--) {
        for (int j = 1; j <= n; j++) {
            cout << a[i][j] << " ";
        }
        cout << endl;
}

2、左右（水平）翻转规律：列下标反转
    for (int i = 1; i <= n; i++) {
        for (int j = n; j >= 1; j--) {
            cout << a[i][j] << " ";
        }
        cout << endl;
    }

3、矩阵转置（对角线翻转）规律：行列下标对调
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            cout << a[j][i] << " ";
        }
        cout << endl;
    }

4、顺时针旋转90度规律：对角线翻转+左右翻转

5、逆时针旋转90度规律：对角线翻转+上下翻转