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, according to set lending rates calculated on the total amount of each payment and repayment, and marked one of the repayment of principal and the respective numbers of interest.