#@@@@#gao shou?

double型
w*x+z-y分解为:
w*x//char*int=int*int,得到一个int型数值
w*x+z//char*int+double=int+double=double,得到一个double型数值
w*x+z-y//char*int+double-float=int+double-float=double-float=double,得到一个double型数值
类型转换顺序:
char->unsigned char->short->unsigned short->long->unsigned long->float->double