#day.rb month = [0,31,28,31,30,31,30,31,31,30,31,30] day = ["日曜日","月曜日","火曜日","水曜日","木曜日","金曜日","土曜日"] a = 0 for i in 0..ARGV[0].to_i-1 a += month[i] end print "その日は ", day[(a + ARGV[1].to_i) % 7], " です\n"
$ ruby day.rb 8 31
のように入力してください。