I am developing a simple C++ application in VS2015. I am getting the error message "Cannot open source file "math". So I right click the project in the solution explorer and navigate to the VC++ Directories, click the "Include Directories" entry in the right-hand pane, pull down the combo box and choose "".
The "Include Directories" dialog appears and is completely read only. I can click the "Macros>>" button and see a list of include macros, but there is no way to add them to your project.
All configuration-dependant properties, including the INCLUDE, are edited in the property-sheets: