If a developer has created a header file then he should use " " and also should include the path while compiling the code.
In company level project, it is very common to find user defined header files and use of " " in .c files .
Double quotes " " instructs compiler to search for header files in user defined path and look into standard path if header file is not found. Angular brace <> is used when a standard header file is included in a program. And compiler also looks into standard path of header file.