endl

std::endl vs \n

#include <iostream>

#ifdef NDEBUG
inline std::ostream& finish(std::ostream& os)
{
    return (os << std::endl);
}
#else
inline std::ostream& finish(std::ostream& os)
{
    return (os << '\n');
}
#endif

using namespace std;

int main(int argc, char** argv)
{
    cout << "Line 1" << finish << "Line 2" << finish;

    return 0;
}