cannot compile and run in ubuntu 18.04

[Hrishikesh Bhandari]

VehicleDetection.cpp:62:4: error: expected primary-expression before ‘->’ token
cv->BackgroundSubtractorMOG2 bg(100, 150, false); // history is an int, distance_threshold is an int (usually set to 16), shadow_detection is a bool
^~
VehicleDetection.cpp:63:2: error: ‘bg’ was not declared in this scope
bg(frame, fore, -1); //learning_rate = -1 here

get this error when i try to compile the code

and also cannot run the compiled file because it requires libopencv version compatible with ubuntu 16.04