(* 目的：時間を受け取ったら午前か午後かを返す *) 
(* jikan : int -> string *) 
let jikan ji = 
  if ji < 12 then "午前" else "午後" 
 
(* テスト *) 
let test1 = jikan 0 = "午前" 
let test2 = jikan 3 = "午前" 
let test3 = jikan 12 = "午後" 
let test4 = jikan 15 = "午後" 
let test5 = jikan 21 = "午後"