Ttykuu

I'm currently undertaking a training course to try & further develop my skills in C#. The latest exercise was to create a basic stopwatch class that meets the following criteria -

Design a class called Stopwatch. The job of this class is to simulate
a stopwatch. It should provide two methods: Start and Stop. We call
the start method first, and the stop method next. Then we ask the
stopwatch about the duration between start and stop. Duration should
be a value in TimeSpan. Display the duration on the console. We should
also be able to use a stopwatch multiple times. So we may start and
stop it and then start and stop it again. Make sure the duration value
each time is calculated properly. We should not be able to start a
stopwatch twice in a row (because that may overwrite the initial start
time). So the class should throw an InvalidOperationException if its
started twice.

Educational tip: The aim of this exercise is to make you understand
that a class should be always in a valid state. We use encapsulation
and information hiding to achieve that. The class should not reveal
its implementation detail. It only reveals a little bit, like a
blackbox. From the outside, you should not be able to misuse a class
because you shouldn’t be able to see the implementation detail.

I'm sure someone is bound to mention it, but yes I'm aware that there is already a stopwatch class in the .NET framework, but as this was the exercise I wanted to try & accomplish it based on the requirements.

The class is as follows -

public class Stopwatch

 private TimeSpan _duration;
 private TimeSpan _start;

 public Stopwatch()
 
 ZeroStart();
 

 public void Start()
 
 if (_start != TimeSpan.Zero)
 throw new InvalidOperationException("The stopwatch has already been started.");

 _start = DateTime.Now.TimeOfDay;
 

 public TimeSpan Stop()
 
 if (_start == TimeSpan.Zero)
 throw new InvalidOperationException("The stopwatch has not been started.");

 _duration = DateTime.Now.TimeOfDay - _start;
 ZeroStart();
 return _duration;
 

 private void ZeroStart()
 
 _start = TimeSpan.Zero;
 

I haven't done an awful lot of OOP or even effective work with classes. Most of the stuff I have done in the past has been more procedural based stuff, just a long list of static methods in static classes etc...

I'm not sure if this is really enough to go on for anyone to actually critique me on so I'm sorry if that's the case.

I've tested the code using the following -

class Program

 static void Main(string[] args)
 
 UsingStopwatch();
 

 static void UsingStopwatch()
 
 Console.WriteLine("This is a stop watch. Type 'start' to start it & 'stop' to stop it.");
 var stopwatch = new Stopwatch();

 while (true)
 
 var input = Console.ReadLine();

 switch (input.ToLower())
 
 case "start":
 stopwatch.Start();
 break;
 case "stop":
 Console.WriteLine(stopwatch.Stop());
 break;
 default:
 Console.WriteLine("Sorry I don't recognize that.");
 break;