4/23 C++: class template (Vector)

#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;

template <typename T>
class Vector{
    private:
        // 資料(變數部分)
        T _x;
        T _y;

    public:
        // 操作(函式部分)

        Vector(){
            _x = 0;
            _y = 0;
        }

        Vector(T x, T y){
            _x = x;
            _y = y;
        }


        // this指標: 指向自己這個物件
        Vector& setX(T x){
            // (*this)._x = x;
            this->_x = x;

            return *this;
        }

        Vector& setY(T y){
            _y = y;
            return *this;
        }

        T getX() const{
            return _x;
        }

        T getY() const{
            return _y;
        }

        double length() const{
            return sqrt( _x * _x + _y * _y );
        }

        Vector operator+(const Vector &b) const{
            double newX = _x + b._x;
            double newY = _y + b._y;
            Vector c(newX, newY);
            return c;
        }

        bool operator<(const Vector &b) const{
            if( length() < b.length() ){
                return true;
            }
            else if( length() > b.length() ){
                return false;
            }
            else if( _x < b._x ){
                return true;
            }
            else if( _x > b._x ){
                return false;
            }
            else if( _y < b._y ){
                return true;
            }
            else if( _y > b._y ){
                return false;
            }
            else{
                return false;
            }
        }

        void print() const{
            cout << "(" << _x << "," << _y << ")" << endl;
        }
};

int main(){

    /*
    const Vector v(3, 4);
    cout << v.length() << endl;
    */


    /*
    Vector<double> a;
    Vector<double> b(-1.2, 6.3);
    a.setX(3).setY(4);

    Vector<double> answer = a + b;// a.operator+(b);
    answer.print();
    */

    Vector<int> array[] = { Vector<int>(3, 4), Vector<int>(4, 5), Vector<int>(1, 2), Vector<int>(3, 5), Vector<int>(1, 3)};

    sort(array, array+5);

    for( int i = 0 ; i < 5 ; i++ ){
        array[i].print();
    }

    return 0;
}