Why not you simply put the decimal integer into the original string as compared to the format specifier?

Answer 1

You can certainly do that ...

printf ("This is a number: 12345\n");

... but that does not have the same value as placing the value in a variable and converting the variable into a string ...

int i = 12345;

printf ("This is a number: %d\n", i);

That's the whole point of format specifiers - to initiate a conversion from one place to another.

Answer 2

Format specifiers are intended to handle variables, not literals.

The following string uses a literal:

"The answer to life, the universe and everything is 42."

The following uses variables:

"A rectangle of width %d units and height %d units has an area of %d square units."