c++中整数的第一位和最后一位数字之和

#include <iostream>
#include <string>

int main() {
    int num = 12345;
    std::string numStr = std::to_string(num);
    int firstDigit = std::stoi(numStr.substr(0, 1));
    int lastDigit = std::stoi(numStr.substr(numStr.length() - 1, 1));
    int sum = firstDigit + lastDigit;
    
    std::cout << "The sum of the first and last digit of " << num << " is " << sum << std::endl;
    
    return 0;
}