Is it possible to write code using c without a header file?

Question

I intend to write in lowest level of computer programming as a hobby, any suggestion how to start.

Tagging as C as I dont know the tag.

Answer 1

It is depend on compiler. Some compilers are smart so that even you have not specified any header file and it will go to default path for header files and search for prototype.

I wrote a sample code and compiled:

int main()
{
   printf("Hello world\n");
   return 0;
}

warning: incompatible implicit declaration of built-in function âprintfâ

Answer 2

For GCC,,,

In headerfile you may have Declaration of functions, Defination(body) of functions, structures, and etc,
so its depend upon progamm , if declaration is not ther then copiler will show Warning but you can run your programm, but if you are using your headerfile for defination for function or structure then you wil get an error in LINKER stage.

I hope i have cleared your doubt.