there's no explanation in this topic why to print a percentage sign one must type %% and not for example escape character with percentage - \%.
from comp.lang.c FAQ list · Question 12.6 :
The reason it's tricky to print % signs with printf is that % is
essentially printf's escape character. Whenever printf sees a %, it
expects it to be followed by a character telling it what to do next.
The two-character sequence %% is defined to print a single %.
To understand why \% can't work, remember that the backslash \ is the
compiler's escape character, and controls how the compiler interprets
source code characters at compile time. In this case, however, we want
to control how printf interprets its format string at run-time. As far
as the compiler is concerned, the escape sequence \% is undefined, and
probably results in a single % character. It would be unlikely for
both the \ and the % to make it through to printf, even if printf were
prepared to treat the \ specially.
so the reason why one must type printf("%%"); to print single % is that's what is defined in printf function. % is an escape character of printf's, and \ of compiler.
