Game randomly chooses number between 1 and 100 (or another range)
User tries to guess the number
Give them hints (e.g. "Colder/Warmer", "Cold/Hot", ...)
Count the number of tries
Let them know when they have won and number of tries
A couple other ideas (optional):
Timer -- compute "solve time" for user
Play against computer. Player finishes, then computer goes. See who takes more tries (slow down the computer computation so you can visually see the computer guesses take place).