toledo:~# perl5.9.3 -d /tmp/as.pl main::(/tmp/as.pl:19): for my $n (0.3, 0, -4, 7, 9) { DB<1> c sqrt(0.300000) = 0.547723 sqrt(0.000000) = 0.000000 assertion failed: argument has to be a positive number at /tmp/as.pl line 10. main::my_sqrt(/tmp/as.pl:16): return sqrt($n); DB<1> l 16==> return sqrt($n); 17 } 18 19: for my $n (0.3, 0, -4, 7, 9) { 20: printf "sqrt(%f) = %f\n", $n, my_sqrt($n); 21 } 22 DB<1> p $n -4