As the title says. I have a C++ project, and added 1 C .h file and a C .c source file, but they are having problems because the rest of the project uses a precompiled header
In C++ at least, you can right click on the cpp file itself and hit properties -- this lets you override C/C++ compiler settings for that file only. You can use that to disable precompiled headers for that one file.
Highlight the file in the Solution Explorer and hit Alt+F7. This will bring up the properties for the file; in the "C/C++" section under "Precompiled Headers" you'll find the relevant options. You don't need to worry about the .h files.