设计一个三维流线类 CPline，定义点类 CPt3d ,有3个成员 x,y,z; 1、该类有属性：点坐标数组，点数； 2、该类有方法： a) 在线末尾添加一个点的函数 AppendPt b) 重载运算符 [] ,实现：设置和获取线上某点信息。 c) 重载运算符 = ，实现线的复制赋值； d) 将函数 AppendPt 重载为 + 运算。

下面是实现 CPt3d 类和 CPline 类的代码：

#include <iostream>
#include <vector>

class CPt3d {
public:
    CPt3d(double x = 0, double y = 0, double z = 0) : x_(x), y_(y), z_(z) {}
    double x() const { return x_; }
    double y() const { return y_; }
    double z() const { return z_; }
private:
    double x_, y_, z_;
};

class CPline {
public:
    CPline() : pts_(), n_(0) {}
    void AppendPt(const CPt3d& pt) {
        pts_.push_back(pt);
        ++n_;
    }
    CPt3d& operator[](int i) { return pts_[i]; }
    const CPt3d& operator[](int i) const { return pts_[i]; }
    CPline& operator=(const CPline& other) {
        pts_ = other.pts_;
        n_ = other.n_;
        return *this;
    }
    CPline operator+(const CPt3d& pt) const {
        CPline new_line(*this);
        new_line.AppendPt(pt);
        return new_line;
    }
    int n() const { return n_; }
private:
    std::vector<CPt3d> pts_;
    int n_;
};

int main() {
    CPline line;
    line.AppendPt(CPt3d(0, 0, 0));
    line.AppendPt(CPt3d(1, 0, 0));
    line.AppendPt(CPt3d(1, 1, 0));
    line.AppendPt(CPt3d(0, 1, 0));
    line.AppendPt(CPt3d(0, 1, 1));

    std::cout << "Line points:" << std::endl;
    for (int i = 0; i < line.n(); ++i) {
        std::cout << "(" << line[i].x() << "," << line[i].y() << "," << line[i].z() << ")" << std::endl;
    }

    CPline new_line = line + CPt3d(0, 0, 1);
    std::cout << "New line points:" << std::endl;
    for (int i = 0; i < new_line.n(); ++i) {
        std::cout << "(" << new_line[i].x() << "," << new_line[i].y() << "," << new_line[i].z() << ")" << std::endl;
    }

    return 0;
}

运行结果如下：

Line points:
(0,0,0)
(1,0,0)
(1,1,0)
(0,1,0)
(0,1,1)
New line points:
(0,0,0)
(1,0,0)
(1,1,0)
(0,1,0)
(0,1,1)
(0,0,1)