设计一个简易的自动售货机，它能够完成钱数处理、找零、显示、退币等功能。

（1）用3个键表示3种钱，再用3个键表示3种物品。

（2）用2个数码管显示输入的钱数，再用2个数码管显示所找的钱数，以元为单位

-Design a simple vending machine, the amount of money that it can complete the treatment, give change, display, coin and other functions. (1) with three keys that three kinds of money, and then 3 keys that 3 items. (2) digital display with two inputs of money, and then two digital display to find the money by the number of units in dollars