在 C++ 中，运算符（对于 POD 类型）总是作用于相同类型的对象。
因此，如果它们不相同，则将提升以匹配另一个。
运算结果的类型与操作数相同（转换后）。

if:
either is      long double       other is promoted >      long double
either is           double       other is promoted >           double
either is           float        other is promoted >           float
either is long long unsigned int other is promoted > long long unsigned int
either is long long          int other is promoted > long long          int
either is long      unsigned int other is promoted > long      unsigned int
either is long               int other is promoted > long               int
either is           unsigned int other is promoted >           unsigned int
either is                    int other is promoted >                    int

Otherwise:
both operands are promoted to int

笔记。操作的最小规模是int。所以short/char被提升到int在操作完成之前。

在您的所有表达式中，在执行操作之前将int提升为 a 。float操作的结果是一个float。

int + float =>  float + float = float
int * float =>  float * float = float
float * int =>  float * float = float
int / float =>  float / float = float
float / int =>  float / float = float
int / int                     = int
int ^ float =>  <compiler error>