using System;

public class Program

{

    // entry point to a C# program

    public static void Main()

    {

        // var m = new Money(12.3);  // PRIVATE -> NOT POSSIBLE

        // var m = new Money(); // PRIVATE -> NOT POSSIBLE

        // static method that returns a money instance

        var m1 = Money.FromDoubleValue(12.3);

        Console.WriteLine(m1.ToString());

        var m2 = Money.FromDoubleValue(14.3);

        Console.WriteLine(m2.ToString());

        //now try to pass strings that might have a double value 

        var m3 = Money.FromStringValue("110.44");

        Console.WriteLine(m3.ToString());

        Console.WriteLine(m3.Data); // possible, because of "public" get in auto property

        // m3.Data = 10; 

        // ^... NOT POSSIBLE! 

            // Compilation error (line 21, col 3): The property or indexer 'Money.Data' cannot be used in this context because the set accessor is inaccessible

        // pass an invalid double value > exception (ArgumentException) will be thrown

        var m4 = Money.FromStringValue("1a1a0.44");

    }

}

​

public class Money {

    // private data component (v -> value)

    // changes to auto property (auto implemented property)

    //  see: 

     // https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/auto-implemented-properties

    // private set: we can set the value of the property only in the ctor! Otherwise it's only possible to retrieve the value of the property.

    public double Data {get; private set;}

    // every new Money object will be created by calling one of the "FromXXXValue" methods

    // static method that will return a money object - 

    // here we can also add some checking code (e.g. "value ok?")

    public static Money FromDoubleValue(double d){

      return new Money(d);

    }

    public static Money FromStringValue(string val){

        double temp;

        // more information on tryparse: https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/types/how-to-convert-a-string-to-a-number

        if (Double.TryParse(val, out temp)) // if we can parse the string to a double, return a new money object

        {

            return new Money(temp);

        }

        else 

        {

            throw new ArgumentException("Value " + val + " can't be converted to a double value! No Money object has been created!");

        };

    }

    // private default ctor, so you can't do this outside the class:

        // var m = new Money();

    private Money(){}

    // private ctor, so you can't do this outside the class:

        // var m = new Money(12.3);

    private Money(double val){

      this.Data = val;

    }

    // just overridden ToString method, so we can quickly print our object 

        // the way we want

    public override String ToString(){

        return "Money with value: " + this.Data.ToString();

    }

}