// FILE: voyage1.cxx
// Written by Michael Main (main@colorado.edu) 
// This is a first example of a C++ program.  The program
// computes how long a trip takes.  The primary purpose is
// to llustrate input, output and assignments in C++.
// This version takes relativity into account.

#include <iostream> // Provides cin and cout
#include <cmath>     // Provides sqrt 
using namespace std;

int main( )
{
    double distance;  // The distance for a trip, in light years.
    double speed;     // The speed for a trip, in fraction of c.
    double time_e;    // The time for a trip, in years on Earth.
    double time_v;    // The time for a trip, in years on voyage.
    double tau;       // Einstein's relativistic factor.

    // Read the input.
    cout << "Please type the distance for the trip, in light years: "; 
    cin >> distance;
    cout << "Your distance is " << distance << " light years." << endl;
    cout << "Please type the speed for the trip, as a fraction of c: "; 
    cin >> speed;
    cout << "Your speed is " << speed << " c." << endl;

    // Calculations.
    time_e = distance / speed;
    tau = sqrt(1 - speed*speed);
    time_v = tau * time_e;

    // Print the output.
    cout << "Your trip will take " << time_e << " years on earth." << endl;
    cout << "Your trip will take " << time_v << " years on voyage." << endl;
    cout << "Space-sickness pills are available in the lounge." << endl;

    return 0;
}