标识符：只能以下划线和字母开头，由数字字母下划线组成
关键字： break defaule func interface select case defer go map struct chan else goto package switch const fallthrough if range type continue for import return var
保留字：constants: ture false ioto nil
types: int int8 int16 int32 in64
uint uint8 uint16 uint32 uint64 uintptr
float32 float64 complex128 cinples64
bool byte rune string error
functions:make len cap new append copy close delete
complex real imag
panic recover
变量声明了就必须使用，否则编译不过去