为啥y的值总会多一呢？

#include <iostream>
using namespace std;
class point
{
   int x,y;
public:
    point(){};
    point(int nx,int ny)
    {
        x=nx;
        y=ny;
    }
    void show()
    {
        cout<<"("<<x<<","<<y<<")"<<endl;
    }
    void move_(int a,int b)
    {
        x+=a;
        y+=b;
    }
    void move_(point &a)
    {
        x=a.x;
        y=a.y;
    }
    void operator==(point a)
    {
        if((x==a.x)&&(y==a.y))
            cout<<"是同一点"<<endl;
        else
            cout<<"不是同一点"<<endl;
    }
    void operator+=(point &a)
    {
        x+=a.x;y+=a.y;
    }
    point operator+(point a)
    {
        point add;
        add.x=x+a.x;
        add.y=y+a.y;
        return add;
    }
    void operator++()
    {
       x++;
       y++;
    }
    void operator++(int a=0)
    {
        x++;
        y++;
    }
};
int main()
{
    int x1,x2,y1,y2;
    cin>>x1>>y1>>x2>>y2;
    point a(x1,y2),b(x2,y2);
    a==b;
    a+=b;
    a.show();
    b.show();
    a=a+b;
    a.show();
    a++;
    a.show();
    ++a;
    a.show();
}

输入：
1 1
2 2
理想输出：
不是同一点
(3,3)
(2,2)
(5,5)
(6,6)
(7,7)

帮你修改好了

#include <iostream>

using namespace std;

class point
{
    int x, y;

public:
    point() : x(0), y(0){};
    point(int nx, int ny)
    {
        x = nx;
        y = ny;
    }
    void show()
    {
        cout << "(" << x << "," << y << ")" << endl;
    }
    void move_(int a, int b)
    {
        x += a;
        y += b;
    }
    void move_(point &a)
    {
        x += a.x;
        y += a.y;
    }
    bool operator==(point a) const
    {
        return x == a.x && y == a.y;
    }
    point &operator+=(point &a)
    {
        x += a.x;
        y += a.y;
        return *this;
    }
    point operator+(point a)
    {
        point add = *this;
        add.x = x + a.x;
        add.y = y + a.y;
        return add;
    }
    point &operator++()
    {
        x++;
        y++;
        return *this;
    }
    point operator++(int)
    {
        point t = *this;
        x++;
        y++;
        return t;
    }
};

int main()
{
    int x1, x2, y1, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    point a(x1, y1), b(x2, y2);
    if (a == b)
        cout << "是同一点" << endl;
    else
        cout << "不是同一点" << endl;
    a += b;
    a.show();
    b.show();
    a = a + b;
    a.show();
    a++;
    a.show();
    ++a;
    a.show();
    return 0;
}