只能运算加减乘除取余，能争确处理数值与运算符之间的空格等空白字符，能使痴线在正确表达式之后的任意字符序列都不会影响下一表达式的计算-Math operations can take over, can compete with the operators do deal values ​ ​ such as blank spaces between characters, crazy line on the right to make any of the characters after the sequence of expression does not affect the calculation of the next expression