If I change the main program to this:

Code:
int main()
{

        bigint a, b, c;
        std::string file_name = "data1-1.txt";
        std::ofstream outfile("results.txt");
        std::ifstream infile("data1-1.txt");
        if(infile.is_open())
        {
                        infile >> a >> b;
                        std::cout << a;
                        std::cout << b;
                        std::cout << "+__________________________________________\n";
                        c = a + b;
                        std::cout << c;
                        infile >> a >> b;
                        std::cout << a;
                        std::cout << b;
                        std::cout << "+__________________________________________\n";
                        c = a + b;
                        std::cout << c;
        }
        else std::cout << "Unable to open file: " << file_name << '\n';
        outfile.close();
        infile.close();
        return 0;
}
Everything works fine and I dont get a segmentation fault.