Numeric data type can include optional exponential notation a lowercase e or uppercase e followed by an optional plus or minus sign and then a number . character expressions that are being converted to an exact 数据类型的字符表达式包含可选的指数符号[一个大写或小写的字母e后跟可选的加号( + )或减号( - ) ，然后再跟一个数字] 。
