Try-catch execution flow in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to catch exceptions.

C Sharp (C#)

try {
    int result = 10 / 0;
} catch ([1]) {
    Console.WriteLine("Error caught");
}

Drag options to blanks, or click blank then click option'

Aint

BException

Cstring

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-exception type like int or string in catch.

Leaving catch parentheses empty.

The catch block must specify an exception type like Exception to catch errors.

2fill in blank

medium

Complete the code to execute code regardless of exceptions.

C Sharp (C#)

try {
    Console.WriteLine("Try block");
} catch (Exception e) {
    Console.WriteLine("Catch block");
} [1] {
    Console.WriteLine("Finally block");
}

Drag options to blanks, or click blank then click option'

Aend

Bfinal

Cfinally

Dcleanup

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'final' or 'end' instead of 'finally'.

Omitting the finally block when cleanup is needed.

The finally block runs code no matter if an exception occurs or not.

3fill in blank

hard

Fix the error in the catch block declaration.

C Sharp (C#)

try {
    int[] arr = new int[2];
    Console.WriteLine(arr[5]);
} catch ([1] e) {
    Console.WriteLine("Index error caught");
}

Drag options to blanks, or click blank then click option'

ANullReferenceException

BFormatException

CArgumentException

DIndexOutOfRangeException

Attempts:

3 left

💡 Hint

Common Mistakes

Using NullReferenceException which is for null objects.

Using ArgumentException which is for invalid arguments.

Accessing an invalid array index throws IndexOutOfRangeException.

4fill in blank

hard

Fill both blanks to catch a specific exception and print its message.

C Sharp (C#)

try {
    int x = int.Parse("abc");
} catch ([1] e) {
    Console.WriteLine(e.[2]);
}

Drag options to blanks, or click blank then click option'

AFormatException

BMessage

CStackTrace

DToString()

Attempts:

3 left

💡 Hint

Common Mistakes

Using StackTrace instead of Message for error text.

Catching the wrong exception type.

FormatException is thrown by int.Parse on invalid input; e.Message shows the error text.

5fill in blank

hard

Fill all three blanks to handle division errors and print a custom message.

C Sharp (C#)

try {
    int a = 10, b = 0;
    int c = a [1] b;
} catch ([2] e) {
    Console.WriteLine("Cannot divide by zero: " + e.[3]);
}

Drag options to blanks, or click blank then click option'

A/

BDivideByZeroException

CMessage

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' instead of '/' for division.

Catching the wrong exception type.

Printing StackTrace instead of Message.

Division uses '/', division by zero throws DivideByZeroException, and Message shows the error.

Practice

1. What happens when an exception occurs inside a try block in C#?

easy

A. The program immediately jumps to the catch block to handle the error.

B. The program ignores the error and continues running the try block.

C. The program stops running without executing any further code.

D. The program restarts the try block from the beginning.

Solution

1. Step 1: Understand try-catch flow

   The try block runs code that might cause an error.

2. Step 2: Exception triggers catch block

   If an error happens, control moves to the catch block to handle it.

3. Final Answer:

   The program immediately jumps to the catch block to handle the error. -> Option A

4. Quick Check:

   Exception in try -> catch runs [OK]

Hint: Errors in try always jump to catch block [OK]

Common Mistakes:

• Thinking the program ignores errors in try
• Assuming the program restarts try block
• Believing the program stops without catch

2. Which of the following is the correct syntax to catch an exception in C#?

easy

A. try { /* code */ } catch (ex Exception) { /* handle */ }

B. try { /* code */ } catch Exception ex { /* handle */ }

C. try { /* code */ } catch { Exception ex } { /* handle */ }

D. try { /* code */ } catch (Exception ex) { /* handle */ }

Solution

1. Step 1: Recall correct catch syntax

   The catch block must have parentheses with exception type and variable: catch (Exception ex).

2. Step 2: Identify correct option

   Only try { /* code */ } catch (Exception ex) { /* handle */ } uses the correct syntax with parentheses and exception variable.

3. Final Answer:

   try { /* code */ } catch (Exception ex) { /* handle */ } -> Option D

4. Quick Check:

   Correct catch syntax = catch (Exception ex) [OK]

Hint: Catch needs parentheses with exception type and variable [OK]

Common Mistakes:

• Omitting parentheses around exception
• Swapping exception type and variable order
• Using braces instead of parentheses

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

try {
    Console.WriteLine("Start");
    int x = 5 / 0;
    Console.WriteLine("End");
} catch (DivideByZeroException) {
    Console.WriteLine("Error caught");
}

medium

A. Start\nError caught

B. Error caught

C. Start\nEnd

D. Start

Solution

1. Step 1: Trace code inside try block

   "Start" prints first. Then division by zero causes an exception.

2. Step 2: Exception triggers catch block

   Catch block runs and prints "Error caught". The line after division is skipped.

3. Final Answer:

   Start\nError caught -> Option A

4. Quick Check:

   Exception skips rest of try, catch prints message [OK]

Hint: Exception skips rest of try, catch runs next [OK]

Common Mistakes:

• Assuming 'End' prints after exception
• Thinking catch runs before 'Start'
• Ignoring exception and continuing try

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

try {
    int[] arr = new int[2];
    arr[3] = 10;
} catch (Exception e) {
    Console.WriteLine("Exception caught");
}

medium

A. Array index out of bounds exception is not caught.

B. The catch block syntax is incorrect.

C. The code will throw an exception but catch block handles it correctly.

D. The try block has a syntax error.

Solution

1. Step 1: Analyze the try block code

   Accessing index 3 in an array of size 2 causes an IndexOutOfRangeException.

2. Step 2: Check catch block handling

   Catch block catches all exceptions of type Exception, so it will handle this error and print the message.

3. Final Answer:

   The code will throw an exception but catch block handles it correctly. -> Option C

4. Quick Check:

   Exception thrown and caught properly [OK]

Hint: Catch(Exception e) catches all exceptions [OK]

Common Mistakes:

• Thinking catch syntax is wrong
• Assuming exception is not caught
• Believing try block has syntax error

5. Consider this code:

try {
    Console.WriteLine("A");
    try {
        int y = int.Parse("abc");
    } catch (FormatException) {
        Console.WriteLine("Format error");
    }
    Console.WriteLine("B");
} catch (Exception) {
    Console.WriteLine("General error");
}

What will be the output?

hard

A. A\nGeneral error\nB

B. A\nFormat error\nB

C. Format error\nB

D. A\nB

Solution

1. Step 1: Trace outer try block

   Prints "A" first, then enters inner try block.

2. Step 2: Inner try-catch handles FormatException

   Parsing "abc" causes FormatException, caught by inner catch which prints "Format error".

3. Step 3: Continue outer try after inner catch

   After inner catch, prints "B". Outer catch is not triggered.

4. Final Answer:

   A\nFormat error\nB -> Option B

5. Quick Check:

   Inner catch handles error, outer continues [OK]

Hint: Inner catch handles error, outer try continues after [OK]

Common Mistakes:

• Assuming outer catch runs instead of inner
• Thinking code stops after inner exception
• Missing that 'B' prints after inner catch