c语言中输入一个字符串逆序输出

#include <stdio.h>
void nixu(char* str, int len){
        char temp;
        for(int i = 0; i < (len / 2); i++){
                temp = str[i];
                str[i] = str[len - i - 1];
                str[len - i -1] = temp;
        }
        for(int i = 0; i < len; i++){
                printf("%c", str[i]);
        }
        putchar('\n');
        printf("%s\n", str);
        putchar('\n');
}
int main(int argc, char* argv[]){
        char a[] = "helloworld!";
        nixu(a, sizeof(a) / sizeof(char) - 1);// -1是为了不要将\0带进去交换
        return 0;
}