Floating-point literals use the usual C++ conventions for exponent and fraction 对于指数和小数,浮点字符使用常用的C++约定
Floating-Point literals may also be represented using exponential notation: a real number followed by the letter e ( or E), followed by an optional plus or minus sign, followed by an integer exponent. 此外,还可以使用指数记数法表示浮点型直接量,即实数后跟随字母e或E,后面加上正负号,其后再加一个整型指数。