①C语言的所有的关键字均由小写字母组成,一旦有一个字母大写,其不再是保留字。②根据关键字的作用,C语言的关键字分为四类。数据类型关键字(12个):char, double, enum, float, int, long, short, signed, struct, union, unsigned, void控制语句关键字(12个):break, case, continue, default, do, else, for, goto, if, return, switch, while存储类型关键字(4个):auto, extern, register, static其它关键字(4个):const, sizeof, typedef, volatile