Because you left the country ( cancelled your visa ) in the middle of the  year  you need the form 1040 to cover the  world income during the "resident period" and attache the 1040-NR for any US sourced / connected income during the "Non-Resident" period -- thus  1. avoiding a short tax  year and 2. protecting any non US sourced/connected income from US taxes.  In your case you really could have just used the 1040  ( especially if you met with the INS  and got a sailing permit, thus proving that you are no longer a resident alien ) but it may be safer to file the 1040-NR ( even if all zeroes  for income ) .  Note that you would need to mail in the two returns  ( generally stapled together) and note on the 1040 across the top "DUAL STATUS TAXPAYER "

Thanks a lot!