Practicing Error Handling

The try-catch syntax has an additional syntax which allows us to catch specific types of errors and deal with them separately:

index


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try 
{
    // code
}
catch (ExceptionType errorVarName)
{
    // code
}
catch (ExceptionType errorVarName)
{
    // code
}
...
finally
{
    // code
}

The type Exception we used in the previous chapter simply catches all kinds of errors however there are some subtypes of Exception which catch more specific kinds of errors. Following are some common exception types:

DivideByZeroException: There's a division by zero;
FileNotFoundException: The file we're accessing doesn't exist;
KeyNotFoundException: The dictionary key doesn't exist;
IndexOutOfRangeException: The specified index of an array or list is invalid.

The term errorVarName is a variable which stores the Exception object, and has information like the error message which can be accessed through errorVarName.Message. We can omit that in case we're not using it:

index


              12345678910111213
            
try 
{
    // code
}
catch (ExceptionType)
{
    // code
}
...
finally
{
    // code
}

Here's an example of using this kind of try-catch block:

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using System;

class Program
{
    static void Main(string[] args)
    {
        int[] myArray = { 0, 2, 4, 6, 8, 10 };
        int i = 0;
        
        while (true)
        {
            try
            {
                Console.Write(myArray[i] / i + " ");
                i++;
            }
            catch(DivideByZeroException)
            {
                i++;
            }
            catch(IndexOutOfRangeException)
            {
                break;
            }
        }
    }
}

Now using these concepts. Fill in the blanks with relevant exception types in the following code to complete the challenge.

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using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        int[] numbers = { 1, 2, 5, 7, 9 };
        var numberNames = new Dictionary<int, string>();

        numberNames.Add(1, "One");
        numberNames.Add(2, "Two");
        numberNames.Add(5, "Five");
        numberNames.Add(9, "Nine");

        int i = 0;
        while (true)
        {
            try
            {
                int key = numbers[i];
                Console.WriteLine($"{key} is {numberNames[key]}");
                i++;
            }
            catch (___)
            {
                break;
            }
            catch (___)
            {
                numberNames.Add(7, "Seven");
            }
        }
    }
}

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Seção 1. Capítulo 10