Reason behind the solution to the question

Question

What is the output of the following and what's the reason behind this?

main()
{
    printf("%%%%");
}

The answer is "%%", but I don't know why.

Answer 1

% is the beginning of a format-specifier. (For example, "%d" means "print an int".) A % after the format-specifier escapes it, printing a single "%".

That is, in the same way "\\" results in a single backslash, "%%" results in a single percent-sign.

Answer 2

in printf, % is usually used to indicate a token such as %s or %d or %5.2f. If you want to output a literal %, you use %%.

Answer 3

Technically, the output could be anything since you didn't print a newline at the end, and also because you didn't include stdio.h :-).

However, correcting the two mistakes:

#include <stdio.h>

int main(void)
{
    printf("%%%%\n");
    return 0;
}

The above should print %% followed by a newline.

Each conversion specification is introduced by the character %.

...

The conversion specifiers and their meanings are:

...

%: A % character is written. No argument is converted. The complete conversion specification shall be %%.

(C99 7.19.6.1).

Answer 4

Format specifiers are typically introduced by a % character,
and a literal percent sign can be copied into the output 
using the escape sequence %%.

Source.

Thus you can print % in the output using %%. The question has a series of % symbols, hence the output is %%.