package mainimport (    "fmt")func main() {    str := "hellOWorlD" //返回str is all lower char    b := make([]byte, len(str))    for i, _:= range str{        s := str[i]        if 'A' <= s && s <= 'Z' {            s = s - 'A' + 'a'        }        b[i] = s    }    fmt.Println(str) //返回hellOWorlD    fmt.Printf("%s\n",b) //返回helloworld}