C++20th Code (Constant by #define) -->Not prefere

    #include<iostream>
    using namespace std;
    #include<iomanip>
    #define con 3.1415926535897932384626433832795
    int main()
    {
    cout<<fixed<<setprecision(15);
    cout<<con<<endl;
    cin.get();
    return con;
    }