fatal error C1083: Cannot open include file: 'd3dx9.h'

or I'm stupid or I do not know
I downloaded the source ins0mnia and when compiling it constantly pops up:
fatal error C1083: Cannot open include file: 'd3dx9.h'
how to add d3dx9.h?

Get the DirectX SDK and include it in the project settings.

were did you find the source to ins0mnia i cant find it

Project -> (Project Name) - Properties -> VC++ Directories (or w/e it's called for you) -> And then include the corresponding folders to the include and library fields