** 23 coins:
You try to buy 23 items, for 23.00 coins.
You buy 23 items for 23.00 coins. You have 77 coins left

** 102 coins:
You try to buy 102 items, for 102.00 coins.
You have not enough money

** -3 coins:
You try to buy -3 items, for -3.00 coins.
Invalid number

** nan coins:
You try to buy nan items, for nan coins.
You buy nan items for nan coins. You have nan coins left