设计一个计算房屋贷款的计算器，要求用户输入房屋每平米单价、房屋面积、首付数目，根据设定的贷款利率来计算月还款额和总还款额，并标出其中还款的本金和利息分别有多少。-The design of a calculation of housing loans calculators, require users to enter unit price per square meter of housing, housing area, the number of down payment, accord