recursion

I was hoping someone could please walk me through on how this works.

Code:

/* Code that accepts a user number and puts it into a function to_binary */

void to_binary(int n)
{
    int r;

    r = n % 2;
    if (n >= 2)
        to_binary(n/2);
    putchar('0' + r);
    return;
}

could you mentally execute the program for
n = 0, 1, 2, 3, 4... ?

ok so 0 and 1 i get.. it prints out either 0 or 01

now lets take 2 for example.. r = 0
2 is = to 2 so 2 / 2 is 1
now r =1 r is < 2 so it prints 01

but thats wrong. how am i looking at this wrong?

now r =1 r is < 2 so it prints 01

No, it calls to_binary(1) before printing the current result, so the final output is '10' as expected.
Each digit is processed from the left to the right and then everything is printed in the
reversed order.