The reference
https://www.gnu.org/software/gnu-c-manual/
https://gcc.gnu.org/onlinedocs/gcc-2.95.3/cpp_toc.html#SEC_Contents
http://www.iu.hio.no/~mark/CTutorial/CTutorial.html
Well done!
https://www.programiz.com/c-programming
http://fresh2refresh.com/c-programming/
A lot of about C books thanks to Mr. Kute T. B.
https://sites.google.com/site/cprbooksite/
//Cairo
//Menehune
El rincón del C
http://www.elrincondelc.com/nuevorincon/index.php
Programacion UTN-FRA
http://www.programacionutn.com.ar/links
Sanfoundry
Loirak
SDL / SDL2
https://wiki.libsdl.org/Tutorials
https://wiki.libsdl.org/SDL_Init
http://lazyfoo.net/tutorials/SDL/01_hello_SDL/linux/cli/index.php