/**
 * Assignment #2, Program 2
 * Program to calculate cyclist's rate of acceleration
 * Author: Mark Allen Weiss
 * SSN: 000-00-0000
 * Course: COP-2210 Section 8
 * Date: September 28, 1998
 *
 * CERTIFICATION OF SOLE AUTHORSHIP
 * I certify that this work is solely my own and
 * that none if it is the work of any other person.
 * I further certify that I have not provided any
 * assistance to other students enrolled in COP-2210 that
 * would render their CERTIFICATION OF SOLE AUTHORSHIP
 * invalid. I understand that violations of this pledge
 * may result in severe sanctions.
 *
 *
 *
 * -----------------------------------
 *   (Mark Allen Weiss)       <--- Put your name here, and sign above
 */

#include <iostream.h>
#include "apstring.h"

  // Function declarations
void display_instructions( );
double get_input( apstring message );
double compute_rate_of_deceleration( double final_velocity,
                               double initial_velocity, double time_interval );
double time_to_rest( double initial_velocity, double rate_of_deceleration );
void print_answers( double rate_of_deceleration, double stopping_time );


int main( )
{
      // Inputs
    double initial_velocity;
    double final_velocity;
    double time_interval;

      // Outputs
    double rate_of_deceleration;
    double stopping_time;

      // Read values
    display_instructions( );
    initial_velocity = get_input( "initial velocity" );
    final_velocity   = get_input( "final velocity" );
    time_interval    = get_input( "time interval" );

      // Compute answers
    rate_of_deceleration = compute_rate_of_deceleration( final_velocity,
                                       initial_velocity, time_interval );
    stopping_time = time_to_rest( initial_velocity, rate_of_deceleration );

      // Print the answers
    print_answers( rate_of_deceleration, stopping_time );

    return 0;
}

/**
 * Print instructions.
 */
void display_instructions( )
{
    cout << "This program will compute the total time it takes for" << endl;
    cout << "a cyclist to stop, given three parameters:" << endl;
    cout << "\t1. An initial velocity" << endl;
    cout << "\t2. A slower velocity" << endl;
    cout << "\t3. The time between the two measurement points above." << endl;
    cout << "Stopping time is from the initial ";
    cout << "velocity until velocity of 0." << endl;
    cout << "The program will also compute the rate of deceleration."
         << endl << endl;
}

/**
 * Print answers.
 */
void print_answers( double rate_of_deceleration, double stopping_time )
{
    cout << endl;
    cout << "The rate of deceleration is " << rate_of_deceleration << endl;
    cout << "The time to stop, measured from the point of initial velocity is "
         << stopping_time << endl;
}

/**
 * Read an input; message is used to give a prompt.
 */
double get_input( apstring message )
{
    double value_read;

    cout << "Please enter " << message << ": ";
    cin >> value_read;

    return value_read;
}

/**
 * Compute the rate of deceleration. This is a positive
 * number if we are decelerating.
 */
double compute_rate_of_deceleration( double final_velocity,
                               double initial_velocity, double time_interval )
{
    return ( initial_velocity - final_velocity ) / time_interval;
}
    
/**
 * Compute the time to rest.
 * Since a = (vf - vi) / t, it follows that
 * t = (vf - vi) / a. By definition, vf = 0, so
 * t = -vi / a, and since deceleration is given by -a,
 * t = vi / d.
 */
double time_to_rest( double initial_velocity, double rate_of_deceleration )
{
    return initial_velocity / rate_of_deceleration;
}