how to convert very very long integers in the form of strings back to integers in c++ code example

Example 1: string to int c++

#include <iostream>
#include <string>

int main() {

    std::string str = "123";
    int num;

    // using stoi() to store the value of str1 to x
    num = std::stoi(str);

    std::cout << num;

    return 0;
}

Example 2: c++ string to int

atoi( str.c_str() )