View Compilation Error

0_0_17429650_20697.cpp: In function 'bool left(const Point&, const Point&, const Point&)':
0_0_17429650_20697.cpp:35:16: error: invalid initialization of non-const reference of type 'Point&' from an rvalue of type 'Point'
  return cross(b-a,c-b)>=0;}
                ^
0_0_17429650_20697.cpp:18:8: note: in passing argument 1 of 'double cross(Point&, Point&)'
 double cross(Point &a, Point &b){
        ^