#include <iostream>
#include <algorithm>

std::string zu_string(int x)
{
    std::string fertig;
    do
        fertig.push_back(x % 10 + '0');
    while(x /= 10);
    std::reverse(fertig.begin(), fertig.end());
    return fertig;
}

std::string operator+(const std::string& b, int a)
{
    return (b + zu_string(a));
}

int main()
{
    std::string x = "123" + 4;
    std::cout << x;
}