c/c++: binary representation of the numeric

I had some free time and remembered old task from the university: show numeric in binary representation. In my old days I'd probably write smth with divs and mods. The core of the algorithm was a mathematical transformation: 13 = 1101 = 2³*1+2²*1+2¹*0+2⁰*1. Now I just have thought about the problem from other side:

int
main()
{
    int n = 13; 

    for (int i=sizeof(n)*8-1;i>=0;--i)
        printf("%d", (n >> i)&1);

    return 0;
}

Here we are:

$gcc 1.c -o out -std=c99 -O2
$./out 
00000000000000000000000000001101

Just fun =).