Can't compile source code from the book C++ for Lazy Programmers

I’ve downloaded the source code from https://github.com/Apress/cpp-for-lazy-programmers of the book C++ for Lazy Programmers by Will Briggs but can’t build the SSDL author developed on SDL.

The error I get when I try to compile the following code;
cpp-for-lazy-programmers/ch1/hello$ make -f Makefile.unix
g++ -c -g sdl2-config --cflags -I…/…/external/SSDL/include main.cpp -o main.o
In file included from …/…/external/SSDL/include/SSDL.h:27,
from main.cpp:7:
…/…/external/SSDL/include/SSDL_display.h:28:10: fatal error: SDL_ttf.h: No such file or directory
28 | #include <SDL_ttf.h>
| ^~~~~~~~~~~
compilation terminated.
make: *** [Makefile.unix:60: main.o] Error 1
I installed SDL2 on my ubuntu 20x and checked the following code to test my installation; https://www.willusher.io/sdl2%20tutorials/2013/08/15/lesson-0-setting-up-sdl
I can’t proceed a bit with the book.
Thank you.

SDL_ttf.h: No such file or directory

(Unix) You’ll need SDL2, SDL2_Image, SDL2_Mixer, and SDL2_TTF installed.

Try a “sudo apt get SDL2_TTF”. or something more precise!