Question

How do I printf integers? When I use:

int n = GetInt();

printf("%n \n", n);

I get the error that there was an unused variable and I can’t compile it.

Answer 1

As the other answers indicated, you normally print an int with the %d conversion specification, or optionally with the %i conversion specification. You can also use %o, %x or %X (and %u), though technically there’s a signed-to-unsigned conversion implied by doing so.

Note that %n is a valid conversion specification for printf() et al. However, unlike all the other conversion specifications, the %n conversion specification is an output operation that takes a pointer to an int and it is used to find out how many characters have been written up to that point in the format string. Therefore, you could use:

int n = GetInt();
int c;

printf("%d%n\n", n, &c);
printf("%d characters in number %d\n", c, n);

Note, too, that there is almost never any need for a space before a newline.

The TR24731-1 (or ISO/IEC 9899:2011 Annex K, Bounds Checking Interfaces) defines printf_s() et al, and explicitly outlaws the %n conversion specification because it often leads to problems precisely because it is an output parameter rather than an input parameter.