C#•3w ago

✅ Exception handling..

namespace Calculator.Model
{
    internal class Division
    {
        public decimal Run(decimal number1, decimal number2)
        {
            if (number2 == 0)
            {
                throw new AlexDivideByZeroException();
            }

            return number1 / number2;
        }

    }
}

namespace Calculator.Model
{
    internal class Division
    {
        public decimal Run(decimal number1, decimal number2)
        {
            if (number2 == 0)
            {
                throw new AlexDivideByZeroException();
            }

            return number1 / number2;
        }

    }
}

When the method Run encounters an instance where number2 == 0 i want it to throw an exception BUT i dont want the program to stop. How does that work?

53 Replies

Jimmacle•3w ago

not sure what you mean the calling code has to handle the exception with a try/catch

Angius•3w ago

You have to catch that exception Otherwise, the program will crash

Merineth 🇸🇪•3w ago

So i have to make a try/catch on the call to run?

Angius•3w ago

Jimmacle•3w ago

yes or somewhere in that call stack so the exception gets caught at some point

Merineth 🇸🇪•3w ago

Right, that does make sense but Ugh it's so hard to explain

public static void ZeroInputArgument()
{
    while (true)
    {

        Console.WriteLine("Enter an RPN expression <return> (empty string = exit):");
        string input = Console.ReadLine();

        // If the input from the user is an empty string, i.e the user pressed Enter. It will close the program.
        if (input == "")
        {
            System.Environment.Exit(1);
        }

        //Vi borde göra om följade till en token klass så att vi inte måste göra detta
        //varenda gång i både zero och two input argument och istället bara kan göra det i en klass.

        //Jag tänker att vi gör en ny klass, typ tokenize, som omvanldlar en 

        //härifrån
        string[] tokens = input.Split(' ');
        Mystack stack = new Mystack();
        stack.Fill(tokens);

        string top = stack.pop();

        CalculationHandler calculationHandler = new CalculationHandler(stack);
        //hit

        decimal output = calculationHandler.Run(top);
        Console.WriteLine("= {0}", output);
    }

public static void ZeroInputArgument()
{
    while (true)
    {

        Console.WriteLine("Enter an RPN expression <return> (empty string = exit):");
        string input = Console.ReadLine();

        // If the input from the user is an empty string, i.e the user pressed Enter. It will close the program.
        if (input == "")
        {
            System.Environment.Exit(1);
        }

        //Vi borde göra om följade till en token klass så att vi inte måste göra detta
        //varenda gång i både zero och two input argument och istället bara kan göra det i en klass.

        //Jag tänker att vi gör en ny klass, typ tokenize, som omvanldlar en 

        //härifrån
        string[] tokens = input.Split(' ');
        Mystack stack = new Mystack();
        stack.Fill(tokens);

        string top = stack.pop();

        CalculationHandler calculationHandler = new CalculationHandler(stack);
        //hit

        decimal output = calculationHandler.Run(top);
        Console.WriteLine("= {0}", output);
    }


In this code here, down towards the bottom we call the

decimal output = calculationHandler.Run(top);


I could make a try/catch here HOWEVER in the output they expect me to list the numbers i'ts trying to divide with. And they are defined elsewhere
e.g

4 0 / should result in console output Exception: Divide by zero: 4,00/0,00`

Jimmacle•3w ago

so put that information in your custom exception and access it in the catch to print that message exceptions are just classes, they can hold whatever data you want

Merineth 🇸🇪•3w ago

I can do that?

Angius•3w ago

So?

try {
    var res = Run();
    Console.WriteLine($"{a} {sig} {b} = {res}");
}
catch(Exception e)
{
    Console.WriteLine($"a = {a}, b = {b} produces {e.Message}");
}

try {
    var res = Run();
    Console.WriteLine($"{a} {sig} {b} = {res}");
}
catch(Exception e)
{
    Console.WriteLine($"a = {a}, b = {b} produces {e.Message}");
}

Or some such Or, yeah, put that info in the exception

Merineth 🇸🇪•3w ago

Can my custom exception print it out?

Angius•3w ago

Exceptions don't "run" So they cannot print You can catch that exception and print whatever's stored in it

Merineth 🇸🇪•3w ago

    internal class Division
    {
        public decimal Run(decimal number1, decimal number2)
        {
            if (number2 == 0)
            {
                throw new AlexDivideByZeroException(number1, number2);
            }
            return number1 / number2;
        }

    }
}

    internal class Division
    {
        public decimal Run(decimal number1, decimal number2)
        {
            if (number2 == 0)
            {
                throw new AlexDivideByZeroException(number1, number2);
            }
            return number1 / number2;
        }

    }
}

Ok so in my division class, if the number2 == 0 i throw a new custom exception with those two numbers

Angius•3w ago

For example, yeah

Merineth 🇸🇪•3w ago

Visual studio made it for me but

    public class AlexDivideByZeroException : Exception
    {
        private decimal number1;
        private decimal number2;

        public AlexDivideByZeroException(decimal number1, decimal number2)
        {
            this.number1 = number1;
            this.number2 = number2;
        }
    }
}

    public class AlexDivideByZeroException : Exception
    {
        private decimal number1;
        private decimal number2;

        public AlexDivideByZeroException(decimal number1, decimal number2)
        {
            this.number1 = number1;
            this.number2 = number2;
        }
    }
}

Seems right?

Pobiega•3w ago

Not quite

Angius•3w ago

It's private How you gonna access that from the outside? Make those private fields into public properties Can be get-only

Pobiega•3w ago

Yep, and maybe call the base constructor to set a message

Merineth 🇸🇪•3w ago

Hold on this is a lot

    public class AlexDivideByZeroException : Exception
    {
        public decimal number1;
        public decimal number2;

        public AlexDivideByZeroException(decimal number1, decimal number2)
        {
            this.number1 = number1;
            this.number2 = number2;
        }
    }
}

    public class AlexDivideByZeroException : Exception
    {
        public decimal number1;
        public decimal number2;

        public AlexDivideByZeroException(decimal number1, decimal number2)
        {
            this.number1 = number1;
            this.number2 = number2;
        }
    }
}

What is the method meant to do?

Angius•3w ago

What method? The constructor? It's... the constructor It's what gets called when you new that thing up

Merineth 🇸🇪•3w ago

haha this course has been so goddamn rushed

MODiX•3w ago

Angius

REPL Result: Success

class Foo
{
    public Foo(string s)
    {
        Console.WriteLine($"Henlo {s}!");
    }
}

var f = new Foo("world");

class Foo
{
    public Foo(string s)
    {
        Console.WriteLine($"Henlo {s}!");
    }
}

var f = new Foo("world");

Console Output

Henlo world!

Henlo world!

Compile: 484.101ms | Execution: 33.981ms | React with ❌ to remove this embed.

Merineth 🇸🇪•3w ago

i feel so overwhelmed How's that a constructor. I was told that is a method.

Angius•3w ago

Look closely It has no return type

Merineth 🇸🇪•3w ago

ah..

Angius•3w ago

And it has the same name as the class It's a constructor $structure

MODiX•3w ago

namespace Namespace;

[Attribute]
public class Class
{
    public string PublicField;
    private bool _privateField;    

    public int PublicProperty { get; set; }

    public Class() {} // Constructor

    public void Method(int parameter)
    {
        var localVariable = parameter; 

        int LocalMethod(string param) { return 3; }
    } 
}

namespace Namespace;

[Attribute]
public class Class
{
    public string PublicField;
    private bool _privateField;    

    public int PublicProperty { get; set; }

    public Class() {} // Constructor

    public void Method(int parameter)
    {
        var localVariable = parameter; 

        int LocalMethod(string param) { return 3; }
    } 
}

Merineth 🇸🇪•3w ago

So constructors are methods without a return type. They just create an object of what's inside the {}?

Angius•3w ago

They let you do the initial setup of the class, basically In your example, the code you sent, it prevents you from ever creating an instance that would not have those two numbers

MODiX•3w ago

Angius

REPL Result: Failure

class Foo
{
    private int _bar;
    public Foo(int bar)
    {
        _bar = bar;
    }
}

var f = new Foo(); // error

class Foo
{
    private int _bar;
    public Foo(int bar)
    {
        _bar = bar;
    }
}

var f = new Foo(); // error

Exception: CompilationErrorException

- There is no argument given that corresponds to the required parameter 'bar' of 'Foo.Foo(int)'

- There is no argument given that corresponds to the required parameter 'bar' of 'Foo.Foo(int)'

Compile: 272.814ms | Execution: 0.000ms | React with ❌ to remove this embed.

Angius•3w ago

One of two ways to ensure the instance will be given all the necessary data when created

Merineth 🇸🇪•3w ago

Yes ok but

    public class AlexDivideByZeroException : Exception
    {
        public decimal number1 { get; }
        public decimal number2 { get; }

        public AlexDivideByZeroException(decimal number1, decimal number2)
        {
            this.number1 = number1;
            this.number2 = number2;
        }
    }
}

    public class AlexDivideByZeroException : Exception
    {
        public decimal number1 { get; }
        public decimal number2 { get; }

        public AlexDivideByZeroException(decimal number1, decimal number2)
        {
            this.number1 = number1;
            this.number2 = number2;
        }
    }
}

` I created my exception for it now

Angius•3w ago

Yep, this will work

Pobiega•3w ago

yep, starting to look good

Angius•3w ago

The naming does not adhere fully to C# standards, but whatever It will do

Merineth 🇸🇪•3w ago

    internal class Division
    {
        public decimal Run(decimal number1, decimal number2)
        {
            if (number2 == 0)
            {
                throw new AlexDivideByZeroException(number1, number2);
            }
            return number1 / number2;
        }

    internal class Division
    {
        public decimal Run(decimal number1, decimal number2)
        {
            if (number2 == 0)
            {
                throw new AlexDivideByZeroException(number1, number2);
            }
            return number1 / number2;
        }

And in my Division class i throw that exception?

Angius•3w ago

Yep

Pobiega•3w ago

so far so good

Merineth 🇸🇪•3w ago

Ok so all the way back

                try
                {
                    decimal output = calculationHandler.Run(top);
                    Console.WriteLine("= {0}", output);
                }
                catch (AlexDivideByZeroException)
                {
                    Console.WriteLine($"Exception: Divide by zero: {number1}/{}");
                }

                try
                {
                    decimal output = calculationHandler.Run(top);
                    Console.WriteLine("= {0}", output);
                }
                catch (AlexDivideByZeroException)
                {
                    Console.WriteLine($"Exception: Divide by zero: {number1}/{}");
                }

How do i access number1 and number2? Because they're still undefined out here

Angius•3w ago

                try
                {
                    decimal output = calculationHandler.Run(top);
                    Console.WriteLine("= {0}", output);
                }
-               catch (AlexDivideByZeroException)
+               catch (AlexDivideByZeroException ex)
                {
                    Console.WriteLine($"Exception: Divide by zero: {number1}/{}");
                }

                try
                {
                    decimal output = calculationHandler.Run(top);
                    Console.WriteLine("= {0}", output);
                }
-               catch (AlexDivideByZeroException)
+               catch (AlexDivideByZeroException ex)
                {
                    Console.WriteLine($"Exception: Divide by zero: {number1}/{}");
                }

That ex will be the instance of your exception And it has those two properties you defined

Merineth 🇸🇪•3w ago

Merineth 🇸🇪•3w ago

Like so?

Angius•3w ago

ex.number1

Merineth 🇸🇪•3w ago

ooh OOOH

Angius•3w ago

ex.number2

Merineth 🇸🇪•3w ago

Okay it's getting way more vividly clear hahah C# is tricky :catHeyHello:

Angius•3w ago

It does make sense in the end, though

Merineth 🇸🇪•3w ago

Yeah just to reiterate what i just did ... I created an Exception called AlexDivideByZeroException which is a subclass of Exception. In the exception we defined 2 fields (i think it's called fields or attributes) We then made a constructor which should hold 2 numbers. We throw a new exception with became an instance?

Angius•3w ago

Two properties, not fields, and certainly not attributes And you did throw a new instance of this exception It did not magically become an instance when throwing

Merineth 🇸🇪•3w ago

right I think i'm getting the hang of it luckily i have to create two more So i can get some more practice 💀

Merineth 🇸🇪•3w ago

So now i'm trying to solve this however 4/3 and A + B result in indexoutofrangeexception But they should be treated differently

Exception: Invalid Operation           4 / 3      
Exception: Invalid token: A            A + B
Exception: Invalid token: &            5 & 6

Merineth 🇸🇪•3w ago

https://tenor.com/view/angry-cat-gif-25783770

Tenor

Merineth 🇸🇪•3w ago

time for a break c: thanks for the help guys 🫶 time to be suicidal

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✅ Exception handling..