在C++中从字符串中提取后4个字符

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello, World!";
    int len = str.length();

    if (len >= 4) {
        std::string lastFour = str.substr(len - 4);
        std::cout << "Last 4 characters: " << lastFour << std::endl;
    } else {
        std::cout << "String is too short to extract 4 characters." << std::endl;
    }

    return 0;
}

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello, World!";
    int len = str.length();
    std::string lastFour = "";

    if (len >= 4) {
        for (int i = len - 4; i < len; ++i) {
            lastFour += str[i];
        }
        std::cout << "Last 4 characters: " << lastFour << std::endl;
    } else {
        std::cout << "String is too short to extract 4 characters." << std::endl;
    }

    return 0;
}

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello, World!";
    int len = str.length();
    std::string lastFour = "";

    if (len >= 4) {
        for (auto it = str.rbegin(); it != str.rbegin() + 4; ++it) {
            lastFour = *it + lastFour;
        }
        std::cout << "Last 4 characters: " << lastFour << std::endl;
    } else {
        std::cout << "String is too short to extract 4 characters." << std::endl;
    }

    return 0;
}