Finally block behavior in C Sharp (C#) - Mini Project: Build & Apply

Finally Block Behavior

📖 Scenario: Imagine you are writing a program that reads a number from a list and divides 100 by that number. Sometimes the number might be zero, which causes an error. You want to make sure that no matter what happens, a message is always shown to say the operation is complete.

🎯 Goal: You will create a program that uses a try, catch, and finally block to handle division by zero errors and always print a completion message.

📋 What You'll Learn

Create an integer array called numbers with the values 10, 0, and 5

Create an integer variable called index and set it to 1

Use a try block to divide 100 by numbers[index] and store the result in result

Use a catch block to catch DivideByZeroException and print "Cannot divide by zero."

Use a finally block to print "Operation complete."

Print the result if no exception occurs

💡 Why This Matters

🌍 Real World

Handling errors safely is important in real programs to avoid crashes and to clean up resources.

💼 Career

Understanding <code>try-catch-finally</code> blocks is essential for writing robust C# applications in many software development jobs.

1

Create the numbers array

Create an integer array called numbers with the values 10, 0, and 5.

C Sharp (C#)

// Your code here

Hint

Use int[] numbers = {10, 0, 5}; to create the array.

2

Set the index variable

Create an integer variable called index and set it to 1.

C Sharp (C#)

int[] numbers = {10, 0, 5};
// Your code here

Hint

Use int index = 1; to set the index.

3

Add try, catch, and finally blocks

Write a try block that divides 100 by numbers[index] and stores the result in an integer variable called result. Add a catch block to catch DivideByZeroException and print "Cannot divide by zero.". Add a finally block that prints "Operation complete.".

C Sharp (C#)

int[] numbers = {10, 0, 5};
int index = 1;
// Your code here

Hint

Use try, catch (DivideByZeroException), and finally blocks as shown.

4

Print the result

Add a line to print the value of result after the try-catch-finally blocks.

C Sharp (C#)

int[] numbers = {10, 0, 5};
int index = 1;
int result = 0;
try
{
    result = 100 / numbers[index];
}
catch (DivideByZeroException)
{
    Console.WriteLine("Cannot divide by zero.");
}
finally
{
    Console.WriteLine("Operation complete.");
}
// Your code here

Hint

Use Console.WriteLine(result); to print the result.

Practice

1. What is the main purpose of the finally block in C# exception handling?

easy

A. To execute code regardless of whether an exception occurs or not

B. To catch exceptions thrown in the try block

C. To declare variables used in the try block

D. To stop the program when an exception occurs

Solution

1. Step 1: Understand the role of finally

   The finally block runs after the try and catch blocks, no matter what happens.

2. Step 2: Identify its purpose

   It is used to run cleanup code or important steps that must always execute, regardless of exceptions.

3. Final Answer:

   To execute code regardless of whether an exception occurs or not -> Option A

4. Quick Check:

   finally always runs [OK]

Hint: Remember: finally always runs, no matter what [OK]

Common Mistakes:

• Confusing finally with catch block
• Thinking finally only runs on exceptions
• Believing finally can catch exceptions

2. Which of the following is the correct syntax for using a finally block in C#?

easy

A. try { } catch { } finally { }

B. try { } finally { } catch { }

C. try { } catch { }

D. finally { } try { } catch { }

Solution

1. Step 1: Recall correct order of blocks

   In C#, the order is try, then catch (optional), then finally (optional).

2. Step 2: Match syntax

   Only try { } catch { } finally { } shows the correct order: try { } catch { } finally { }.

3. Final Answer:

   try { } catch { } finally { } -> Option A

4. Quick Check:

   Correct block order [OK]

Hint: Remember order: try, catch, then finally [OK]

Common Mistakes:

• Placing finally before catch
• Omitting try block
• Using finally without try

3. What will be the output of the following C# code?

try {
    Console.WriteLine("Start");
    throw new Exception();
} catch {
    Console.WriteLine("Caught");
} finally {
    Console.WriteLine("Finally");
}

medium

A. Start\nFinally

B. Start\nCaught\nFinally

C. Caught\nFinally

D. Start\nCaught

Solution

1. Step 1: Trace the try block

   "Start" is printed, then an exception is thrown.

2. Step 2: Catch and finally execution

   The exception is caught, so "Caught" is printed, then the finally block runs printing "Finally".

3. Final Answer:

   Start\nCaught\nFinally -> Option B

4. Quick Check:

   try prints Start, catch prints Caught, finally prints Finally [OK]

Hint: Remember: finally runs after catch even if exception thrown [OK]

Common Mistakes:

• Ignoring catch block output
• Thinking finally runs before catch
• Missing the exception thrown in try

4. Identify the error in this C# code snippet:

try {
    Console.WriteLine("Hello");
} finally {
    Console.WriteLine("Cleanup");
} catch (Exception ex) {
    Console.WriteLine("Error");
}

medium

A. The catch block must come after finally

B. No error, code is correct

C. You cannot use finally without catch

D. The finally block must come after catch

Solution

1. Step 1: Check block order rules

   In C#, the finally block must come after all catch blocks.

2. Step 2: Identify incorrect order

   The code places finally before catch, which is invalid syntax.

3. Final Answer:

   The finally block must come after catch -> Option D

4. Quick Check:

   finally after catch [OK]

Hint: Remember: catch blocks come before finally [OK]

Common Mistakes:

• Placing finally before catch
• Thinking finally can be before catch
• Confusing order of blocks

5. Consider this code:

int result = 0;
try {
    result = 10 / 0;
} catch (DivideByZeroException) {
    result = 1;
} finally {
    result = 2;
}
Console.WriteLine(result);

What will be printed and why?

hard

A. 0, because division by zero stops execution before catch

B. 1, because catch sets result to 1 and finally does not change it

C. 2, because finally always runs and can overwrite result

D. Exception thrown, program crashes

Solution

1. Step 1: Analyze exception and catch block

   Division by zero throws DivideByZeroException, caught by catch which sets result = 1.

2. Step 2: Understand finally block effect

   The finally block runs after catch and sets result = 2, overwriting previous value.

3. Final Answer:

   2, because finally always runs and can overwrite result -> Option C

4. Quick Check:

   finally runs last and sets result = 2 [OK]

Hint: finally runs last and can overwrite variables set earlier [OK]

Common Mistakes:

• Assuming catch value stays after finally
• Thinking exception stops finally from running
• Believing program crashes without output