# Include <> and # include ""

<> Reference the header file in the compiler's class library path.
"" References the header file in the relative path of your program directory.

Assume that the header file defined by your compiler is referenced in c: \ Keil \ C51 \ Inc \.
Then # include references the header file c: \ Keil \ C51 \ Inc \ stdio. h.
No matter what directory your project is in, set the path c: \ Keil \ C51 \ Inc \ stdio. h.
It generally refers to some built-in header files: stdio. H, conio. H, String. H, stdlib. H, and so on ..

Assume that your project directory is in D: \ projects \ TMP \
Then # include "My. H" references the header file D: \ projects \ TMP \ My. h.
It is generally used to reference some header files that you write.
If "" is used, it will first find whether the corresponding header file exists in the current directory of your project.
If no, it will still find the corresponding header file in the corresponding reference directory
That is, use # include "stdio. H "if there is no stdio in your project directory. h. The header file will still be located in C: \ Keil \ C51 \ Inc \ stdio. h header file

# Include <> and # include ""