I want to make the basic trigonometric functions in maths inbuilt functions using my own header file . so as the users can do trigonometry in c language compilers.
You can't make new functions "built-in" to C without changing the compiler. However, you can write and extend libraries with new functions that your programs can then reuse wherever they want. For that, you need to compile a library with the functions, your program needs to include the library header file, and the linker has to include the object code for your functions. Please elaborate if you need more specific help.