I followed the exact tutorial on the website. Here is what I did for the installation:

Download and unzip the pre-compiled 3.1.0 package.

In the command window: setx -m OPENCV_DIR C:\opencv310\Build\x64\vc14

Add %OPENCV_DIR%\bin to path in the system variable.

After setting environment variable I followed the tutorial:

c/c++--additional include directories: $(OPENCV_DIR)....\include for both debug and release mode

linker--general--additional library directories: $(OPENCV_DIR)\lib for both debug and release mode

linker--input--additional dependencies: opencv_world310d.lib for debug mode; opencv_world310.lib for release mode

However,

include <opencv2\opencv.hpp>

gave an error saying no such file or directory. Can someone help me?