字符串逆序

 void revert(char* str) {
`    char c;
`    for (int front = 0, int back = strlen(str) - 1;
`         front < back;
`         ++front, --back) {
`      c = str[back];
`      str[back] = str[front];
`      str[front] = c;
`    }
` }