复合赋值运算符
一、
a *= b + 6;
意味着 a = a * ( b + 6 );
须要注意运算符的优先级;
二、
a = i++;
a = ++i;
若i = 6,则
a = i++ → a = 6,i = 7;后缀,a先等于i
a = ++i → a = 7,i = 7;前缀,