Question

Given code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ClassLibrary1
{
public class Car
{
// fields
private decimal _CurrentSpeedMPH; // the cars current speed
private decimal _MaxSpeedMPH; // the upper limit, the car cannot exceed this value
private bool _EngineRunning; // true means the engine has been started and is running, false says engine is off

public Car(decimal maxSpeed) // constuctor, user chooses to set maxSpeed as they create the object
{
_MaxSpeedMPH = maxSpeed;
_CurrentSpeedMPH = 0;
_EngineRunning = false;
}

  
public bool EngineRunning // Property to allow reading the current value
{ get { return _EngineRunning; } }

public decimal CurrentSpeedMPH // Property to allow reading the current value
{ get { return _CurrentSpeedMPH; } }

public void StartEngine() // method used to start car's engine
{
_EngineRunning = true;
}

public void StopEngine() // method used to stop car's engine
{
_EngineRunning = false;
}

public void Accelerate() // method used to increase the cars speed
{
_CurrentSpeedMPH = _CurrentSpeedMPH + 10; // this method always tries to increase by 10 mph
if (_CurrentSpeedMPH > _MaxSpeedMPH) // but it can never exceed the max speed as set in the constructor
{
_CurrentSpeedMPH = _MaxSpeedMPH; // if speed is higher than max, slow it to max
}
}

public void Decelerate() // this method always tries to decrease the speed by 5 mph
{
_CurrentSpeedMPH = _CurrentSpeedMPH - 5; // but never lets it go below 0 and become negative.
if (_CurrentSpeedMPH < 0)
{
_CurrentSpeedMPH = 0;
}
}
}
}

First, modify the car class to throw 3 new exceptions

[1] In the Modify the StartEngine method:

              Change the logic such that if the user code calls the StartEngine method when the engine is already started, the StartEngine method will throw a new ApplicationException and that exception should have a Message property set to “Engine is already started.”.

[2] Modify the StopEngine method:

              Change the logic such that if the user code calls the StopEngine engine when the engine is already stopped, the StopEngine method will throw a new ApplicationException and that exception should have a Message property set to “Engine is not running.”.

[3] Modify the Accelerate method:

              Change the logic such that if the user code gives calls the Accelerate method when the engine is not running, the Accelerate method will throw new ApplicationException and that exception should have a Message property set to “Please start engine.”. (Note that braking should work even if the engine is on or off, so no change is needed for that code.)

[4] Run your program now, and try these 3 nonsensical things (trying to accelerate when the engine is not running, trying to start the engine when it is already started, and trying to stop the engine when it is already stopped) and verify the system pops up “uncaught exception” boxes showing each of your 3 unique error messages.

Answer 1

Working code implemented in C# and appropriate comments provided for better understanding.

Here I am attaching code for all files:

• Cars.cs
• Program.cs

Cars.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ClassLibrary1
{
public class Car
{
// fields
private decimal _CurrentSpeedMPH; // the cars current speed
private decimal _MaxSpeedMPH; // the upper limit, the car cannot exceed this value
private bool _EngineRunning; // true means the engine has been started and is running, false says engine is off

public Car(decimal maxSpeed) // constuctor, user chooses to set maxSpeed as they create the object
{
_MaxSpeedMPH = maxSpeed;
_CurrentSpeedMPH = 0;
_EngineRunning = false;
}

  
public bool EngineRunning // Property to allow reading the current value
{ get { return _EngineRunning; } }

public decimal CurrentSpeedMPH // Property to allow reading the current value
{ get { return _CurrentSpeedMPH; } }

  
public void StartEngine() // method used to start car's engine
{
//Throw application exception when engine is already running
if (_EngineRunning)
{
throw new ApplicationException("Engine is already started.");
}
else
{
_EngineRunning = true;
}
}

public void StopEngine() // method used to stop car's engine
{
//Throw application exception when current speed in miles per hour is not zero
if (_CurrentSpeedMPH != 0)
{
throw new ApplicationException("Please stop car first.");
}
else
{
_EngineRunning = false;
}
  
}

public void Accelerate() // method used to increase the cars speed
{
//Throw application exception when the engine is not running
if (!_EngineRunning)
{
throw new ApplicationException("Please start engine.");
}
else
{
_CurrentSpeedMPH = _CurrentSpeedMPH + 10; // this method always tries to increase by 10 mph
if (_CurrentSpeedMPH > _MaxSpeedMPH) // but it can never exceed the max speed as set in the constructor
{
_CurrentSpeedMPH = _MaxSpeedMPH; // if speed is higher than max, slow it to max
}
}
}

public void Decelerate() // this method always tries to decrease the speed by 5 mph
{
_CurrentSpeedMPH = _CurrentSpeedMPH - 5; // but never lets it go below 0 and become negative.
if (_CurrentSpeedMPH < 0)
{
_CurrentSpeedMPH = 0;
}
}

}
}

Program.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using ClassLibrary1;

namespace ConsoleCarsExcpeptions
{
class Program
{
static void Main(string[] args)
{
Car myCar = new Car(35); // call constructor and set speed max to 35 (tiny engine!!)
string ErrorMessage = "All is well";

// Put try / catch over switch in while loop to catch throws from car class and to set ErrorMessage
bool bHadError = false; // to check if we had an error this loop
bool done = false; // loop control variable
while (!done)
{
Console.WriteLine();
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine("start = start engine, stop = stop engine");
Console.Write("accel = accelerate, brake = brake, q = quit. Command? :");
Console.ResetColor();
string userInput = Console.ReadLine();
userInput = userInput.ToLower(); // in case user happened to enter capital letters
Console.Clear(); // each time we get a new command, clear the prior history from the console

try
{

switch (userInput)
{
case "start":
myCar.StartEngine();
break;
case "stop":
myCar.StopEngine();
break;
case "accel":
myCar.Accelerate();
break;
case "brake":
myCar.Decelerate();
break;
case "q":
case "e":
Console.WriteLine("Goodbye");
done = true;
break;
default:
Console.WriteLine("Not a valid input.");
break;
} // end switch

}// end try
catch (ApplicationException ex)
{
// Set the ErrorMessage to exceptions message,
// and set error flag to true so we can reset after we display error.
ErrorMessage = ex.Message;
bHadError = true;

} // end catch

// at the end of each command, call this method to show status
DisplayCarState(ErrorMessage, myCar);

if (bHadError) // reset error message now
{
// Reset ErrorMessage to "All is well" and reset error flag
ErrorMessage = "All is well";
bHadError = false;
}
}// end while
Console.ReadLine();

}// end main

private static void DisplayCarState(string msg, Car myCar)
{
Console.ForegroundColor = ConsoleColor.Magenta;
Console.WriteLine(msg);
Console.WriteLine("Engine is running: " + myCar.EngineRunning);
Console.WriteLine("Current speed is: " + myCar.CurrentSpeedMPH);
Console.ResetColor();
}
}
}

Sample Output Screenshots: