Sockets Practice: portscan.c

I've been working my way through Stevens' Unix Network Programming. One of my non-book exercises has been portscan.c:

dennis@ipa:~/projects/sockets/portscan$ ./portscan -l 127.0.0.1.log 127.0.0.1

Port scanning 127.0.0.1:

Port 13 is open.
Port 22 is open.
Port 25 is open.
Port 37 is open.