Question

What is the correct syntax for this code:
is it:

printf("printf(\"\%d\",%s);", some_var);

or

printf("printf(\"%%d\",%s);", some_var);

Or something else?

Answer 1

The second one. %d is defined by printf, not the C language, so you need to escape it with the printf %%, not a character escape.

A more complex example with a character escape sequence:

printf("printf(\"%%d\\n\",%s);\n", some_var);