Summary - Exception basics

C# course · Beginner · Lesson 111/116

Combine try/catch/finally and a custom exception to write a bank account class.

Summary - Exception basics

In this group you learned the basics of exception handling. The try block holds risky code, catch handles errors, and finally always cleans up. You throw exceptions with throw and rethrow with throw;.

The Exception class's Message, StackTrace and InnerException properties help with debugging. For your domain's specific errors, you can write classes derived from Exception. In the next exercise you will try them all together.

Practical tips

A few tips on exception handling: start with the most specific catch type and leave the most general Exception for last. When rethrowing, use throw; instead of throw ex;. Use finally for resource cleanup.

Define custom exception classes only when you truly need domain-specific handling. Instead of showing the raw stack trace to the user, offer a meaningful message. These tips help you build error handling that is both safe and readable.

Exercise Combine try/catch/finally

Inside a try block, divide with int c = a / b;. In a catch (DivideByZeroException) block, print "Division by zero error" with Console.WriteLine. In a finally block, print "Done" with Console.WriteLine.

Show example solution

Write try { int c = a / b; } catch (DivideByZeroException) { Console.WriteLine("Division by zero error"); } finally { Console.WriteLine("Done"); }
Example solution:
using System;

class Program
{
    static void Main()
    {
        int a = 10;
        int b = 0;
        try
        {
            int c = a / b;
        }
        catch (DivideByZeroException)
        {
            Console.WriteLine("Division by zero error");
        }
        finally
        {
            Console.WriteLine("Done");
        }
    }
}

Test yourself

Match each keyword with its job

try

Risky code
catch

Catches errors
finally

Cleanup
throw

Throws an exception
Which is true for exception handling?
```
try { ... } catch (Exception ex) { ... }
```
- Only try is enough
- try cannot exist without catch
- catch cannot exist without finally
- try and catch are used together
Show answer

try and catch are used together — Correct! try and catch are used together; finally is optional.

Summary - Exception basics