#include <iostream>
#include <fstream>

int main() {
    {   // creation du fichier
        std::ofstream out { "test.txt" };
        out << 123.4546 << std::endl;
        out << 123.456e78 << std::endl;
    }
    
    std::ifstream in { "test.txt" };
    double x {};
    in >> x;
    std::cout << x << std::endl;
    in >> x;
    std::cout << x << std::endl;
    
    return 0;
}