C++ :

#include <iostream>
using namespace std;
int main() {
    char str[100];
    cin.getline(str, 100);
    int length = 0;
    while (str[length] != '\0') {
        length++;
    }
    // 交换字符串首尾字符，直到中间
    for (int i = 0; i < length / 2; i++) {
        char temp = str[i];
        str[i] = str[length - 1 - i];
        str[length - 1 - i] = temp;
    }
    cout << str << endl;
    return 0;
}