Why exception handling is needed in C Sharp (C#) - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to catch an exception.

C Sharp (C#)

try {
    int result = 10 / [1];
} catch (DivideByZeroException) {
    Console.WriteLine("Cannot divide by zero.");
}

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

A0

B1

C2

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-zero number does not cause an exception.

Dividing by zero causes an exception. Catching it prevents the program from crashing.

2fill in blank

medium

Complete the code to throw an exception when input is invalid.

C Sharp (C#)

if (age < 0) {
    throw new [1]("Age cannot be negative.");
}

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

AArgumentException

BArgumentNullException

CInvalidOperationException

DDivideByZeroException

Attempts:

3 left

💡 Hint

Common Mistakes

Using exceptions unrelated to argument errors.

ArgumentException is used when an argument is invalid, like a negative age.

3fill in blank

hard

Fix the error in the catch block to handle any exception.

C Sharp (C#)

try {
    int[] numbers = new int[3];
    int x = numbers[5];
} catch ([1]) {
    Console.WriteLine("An error occurred.");
}

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

AIndexOutOfRangeException

BNullReferenceException

CDivideByZeroException

DException

Attempts:

3 left

💡 Hint

Common Mistakes

Catching only specific exceptions misses others.

Catching Exception handles all exceptions, including unexpected ones.

4fill in blank

hard

Fill both blanks to handle a file error and display a message.

C Sharp (C#)

try {
    var text = System.IO.File.ReadAllText([1]);
} catch ([2]) {
    Console.WriteLine("File not found.");
}

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

A"data.txt"

BFileNotFoundException

CIOException

D"input.txt"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong exception type or missing quotes around filename.

Reading "data.txt" may cause FileNotFoundException if the file is missing.

5fill in blank

hard

Fill all three blanks to catch an exception and print its message.

C Sharp (C#)

try {
    int num = int.Parse([1]);
} catch ([2] ex) {
    Console.WriteLine([3]);
}

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

A"abc"

BFormatException

Cex.Message

D"123"

Attempts:

3 left

💡 Hint

Common Mistakes

Parsing a valid number does not cause exception.

Parsing "abc" causes FormatException. Printing ex.Message shows the error.

Practice

1. Why do we need exception handling in C# programs?

easy

A. To write shorter code

B. To prevent the program from crashing when an error occurs

C. To make the program run faster

D. To avoid using variables

Solution

1. Step 1: Understand what happens without exception handling

   Without exception handling, errors cause the program to stop immediately, which is called crashing.

2. Step 2: Identify the purpose of exception handling

   Exception handling lets the program catch errors and continue running or show helpful messages instead of crashing.

3. Final Answer:

   To prevent the program from crashing when an error occurs -> Option B

4. Quick Check:

   Exception handling prevents crashes = C [OK]

Hint: Exception handling stops crashes and shows messages [OK]

Common Mistakes:

• Thinking exception handling makes code faster
• Confusing exception handling with code optimization
• Believing exception handling removes the need for variables

2. Which of the following is the correct syntax to start handling exceptions in C#?

easy

A. catch { /* code */ } try { /* handle error */ }

B. error { /* code */ } catch { /* handle */ }

C. handle { /* code */ } try { /* error */ }

D. try { /* code */ } catch { /* handle error */ }

Solution

1. Step 1: Recall the structure of exception handling

   In C#, exception handling starts with a try block followed by one or more catch blocks.

2. Step 2: Match the correct syntax

   try { /* code */ } catch { /* handle error */ } correctly shows try { } followed by catch { }. Other options have wrong order or invalid keywords.

3. Final Answer:

   try { /* code */ } catch { /* handle error */ } -> Option D

4. Quick Check:

   try-catch syntax = B [OK]

Hint: Exception handling always starts with try block [OK]

Common Mistakes:

• Putting catch before try
• Using unknown keywords like handle or error
• Missing the try block entirely

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

try {
  int x = 10 / 0;
  Console.WriteLine("Result: " + x);
} catch (DivideByZeroException) {
  Console.WriteLine("Cannot divide by zero.");
}

medium

A. Result: 0

B. No output

C. Cannot divide by zero.

D. Runtime error and program crashes

Solution

1. Step 1: Identify the error in the try block

   The code tries to divide 10 by 0, which causes a DivideByZeroException.

2. Step 2: Check the catch block handling

   The catch block catches DivideByZeroException and prints "Cannot divide by zero." instead of crashing.

3. Final Answer:

   Cannot divide by zero. -> Option C

4. Quick Check:

   Divide by zero caught = D [OK]

Hint: Divide by zero triggers catch block output [OK]

Common Mistakes:

• Expecting program to crash instead of catching error
• Thinking output is 'Result: 0'
• Ignoring the catch block

4. Find the error in this exception handling code:

try {
  int[] arr = new int[3];
  Console.WriteLine(arr[5]);
} catch (IndexOutOfRangeException e) {
  Console.WriteLine("Index error: " + e.Message);
} finally {
  Console.WriteLine("Done.");
}

medium

A. There is no error; code handles exception correctly

B. The finally block is missing

C. The catch block should catch NullReferenceException instead

D. The array size is too big

Solution

1. Step 1: Analyze the try block code

   The code accesses index 5 of an array with size 3, causing an IndexOutOfRangeException.

2. Step 2: Check the catch and finally blocks

   The catch block correctly catches IndexOutOfRangeException and prints a message. The finally block prints "Done." This is correct usage.

3. Final Answer:

   There is no error; code handles exception correctly -> Option A

4. Quick Check:

   Correct catch and finally usage = A [OK]

Hint: Catch correct exception type and use finally for cleanup [OK]

Common Mistakes:

• Catching wrong exception type
• Forgetting finally block
• Assuming array size causes error

5. You want to read a number from user input and handle errors if the input is not a number. Which code snippet correctly uses exception handling to do this?

hard

A. try {
int num = int.Parse(Console.ReadLine());
Console.WriteLine($"You entered {num}");
} catch (FormatException) {
Console.WriteLine("Please enter a valid number.");
}

B. int num = int.Parse(Console.ReadLine());
Console.WriteLine($"You entered {num}");

C. try {
int num = Console.ReadLine();
Console.WriteLine($"You entered {num}");
} catch (Exception) {
Console.WriteLine("Error occurred.");
}

D. try {
int num = Convert.ToInt32(Console.ReadLine());
} finally {
Console.WriteLine("Input processed.");
}

Solution

1. Step 1: Understand the goal

   We want to read a number and catch errors if input is not a valid number.

2. Step 2: Check each option for correct exception handling

   try { int num = int.Parse(Console.ReadLine()); Console.WriteLine($"You entered {num}"); } catch (FormatException) { Console.WriteLine("Please enter a valid number."); } uses try with int.Parse and catches FormatException, which is correct. int num = int.Parse(Console.ReadLine()); Console.WriteLine($"You entered {num}"); has no error handling. try { int num = Console.ReadLine(); Console.WriteLine($"You entered {num}"); } catch (Exception) { Console.WriteLine("Error occurred."); } tries to assign string to int without parsing. try { int num = Convert.ToInt32(Console.ReadLine()); } finally { Console.WriteLine("Input processed."); } uses finally but no catch, so errors are not handled.

3. Final Answer:

   try { int num = int.Parse(Console.ReadLine()); Console.WriteLine($"You entered {num}"); } catch (FormatException) { Console.WriteLine("Please enter a valid number."); } -> Option A

4. Quick Check:

   Try-catch with int.Parse and FormatException = A [OK]

Hint: Use try-catch around int.Parse to catch invalid input [OK]

Common Mistakes:

• Not using try-catch for parsing input
• Assigning string directly to int variable
• Using finally without catch to handle errors