有如下程序：#include ＜iostream＞using namespace std;class point{ int x, y;public: point( int vx, int vy ) { x = vx; y = vy; } point ( ) x = 0; y= 0; } point operator+( point p1 ) { point p; int px = x+ p1.x; int py = y + p1.y; return point( px, py ); point operator-( point p1 ) { point p; int px = x -p1.x; int py = y - p1.y; return point ( px, py ); } void print() { cout＜＜x＜＜" , "＜＜y＜＜end1; }};int main (){ point p1(10, 10 ), p2( 20, 20 ); p1 = p1 - p2; p1.print (); return 0;} 执行后的输出结果是