能进行简单的四则运算，含有小数点功能和清除功能，清除功能包括全部清除和一个一个数字地清除，但是清除小数时只能清除最后面的那个数字。-To carry out simple arithmetic, which contains a decimal point function and clearance, including clearance of all clear and a way to remove a number, but can only be cleared when the c