C: Output "tomorrow's date"
Okay, it's been a while since I wrote any C but I'll give it a go:

m,y,*q="%d/%d/%d";
main(d){
scanf(q,&amp;d,&amp;m,&amp;y);
++d&gt;30+(m+(m&gt;7))%2-(m^2?0:2-!(y%4))?(m+=d=1)&gt;12?y+=m=1:0:0;
printf(q,d,m,y);}


120 characters.
With a bit of formatting(not that it makes it any more readable any more...):

m,y,*q="%d/%d/%d";
main(d)
{
    scanf(q,&amp;d,&amp;m,&amp;y);
    ++d&gt;30+(m+(m&gt;7))%2-(m^2?0:2-!(y%4))?(m+=d=1)&gt;12?y+=m=1:0:0;
    printf(q,d,m,y);
}


The compiler throws out warnings like nobody's business, but it works.

I'm not sure I can get it any smaller than this now without stealing a couple of tricks from Griffin. With those tricks I can get to 116 characters:

m,y,*q="%d/%d/%d";
main(d){
scanf(q,&amp;d,&amp;m,&amp;y);
printf(q,d,m,++d&gt;30+(m&gt;7^m&amp;1)-(m^2?0:2-!(y%4))?(m+=d=1)&gt;12?y+=m=1:y:y);}