Multiple catch blocks in C Sharp (C#) - Mini Project: Build & Apply

Handling Errors with Multiple Catch Blocks in C#

📖 Scenario: Imagine you are writing a simple calculator program that divides two numbers. Sometimes, users might enter zero as the divisor or enter invalid input. You want to handle these errors gracefully.

🎯 Goal: Build a C# program that uses try with multiple catch blocks to handle different types of errors separately.

📋 What You'll Learn

Create two integer variables named numerator and denominator with exact values.

Create a try block to perform division.

Add two catch blocks: one for DivideByZeroException and one for FormatException.

Print the result or error messages accordingly.

💡 Why This Matters

🌍 Real World

Handling errors gracefully is important in real-world programs to avoid crashes and give users helpful messages.

💼 Career

Understanding multiple catch blocks is essential for writing robust C# applications that handle different error types properly.

1

Create numerator and denominator variables

Create two integer variables called numerator and denominator with values 10 and 0 respectively.

C Sharp (C#)

# Your code here

Hint

Use int numerator = 10; and int denominator = 0; to create the variables.

2

Add a try block to divide numerator by denominator

Add a try block that attempts to divide numerator by denominator and stores the result in an integer variable called result.

C Sharp (C#)

int numerator = 10;
int denominator = 0;

// Add try block below
# Your code here

Hint

Use try { int result = numerator / denominator; } to catch errors during division.

3

Add multiple catch blocks for DivideByZeroException and FormatException

Add two catch blocks after the try: one catching DivideByZeroException that prints "Cannot divide by zero.", and another catching FormatException that prints "Invalid input format.".

C Sharp (C#)

int numerator = 10;
int denominator = 0;

try
{
    int result = numerator / denominator;
}

// Add catch blocks below
# Your code here

Hint

Use two separate catch blocks for each exception type with the exact messages.

4

Print the result if division succeeds

Inside the try block, after dividing, add a Console.WriteLine to print "Result: " followed by the result variable.

C Sharp (C#)

int numerator = 10;
int denominator = 0;

try
{
    int result = numerator / denominator;
    // Print the result below
    # Your code here
}
catch (DivideByZeroException)
{
    Console.WriteLine("Cannot divide by zero.");
}
catch (FormatException)
{
    Console.WriteLine("Invalid input format.");
}

Hint

Use Console.WriteLine("Result: " + result); inside the try block.

Practice

1.

What is the main purpose of using multiple catch blocks in C#?

easy

A. To avoid using try blocks

B. To handle different types of exceptions separately

C. To make the code run faster

D. To declare multiple variables

Solution

1. Step 1: Understand the role of catch blocks

   catch blocks are used to handle errors that happen in the try block.

2. Step 2: Recognize why multiple catch blocks are used

   Using multiple catch blocks lets you respond differently to different error types, making your program clearer and safer.

3. Final Answer:

   To handle different types of exceptions separately -> Option B

4. Quick Check:

   Multiple catch blocks = handle different exceptions [OK]

Hint: Multiple catch blocks handle different errors separately [OK]

Common Mistakes:

• Thinking multiple catch blocks speed up code
• Believing catch blocks replace try blocks
• Using catch blocks to declare variables

2.

Which of the following is the correct syntax order for multiple catch blocks in C#?

try { ... }
catch (ArgumentNullException e) { ... }
catch (Exception e) { ... }

easy

A. Specific exceptions first, general exceptions last

B. General exceptions first, specific exceptions last

C. Order does not matter

D. Only one catch block is allowed

Solution

1. Step 1: Understand exception hierarchy

   Specific exceptions like ArgumentNullException inherit from general exceptions like Exception.

2. Step 2: Order catch blocks correctly

   Place specific exceptions first so they catch their errors before the general catch block handles all others.

3. Final Answer:

   Specific exceptions first, general exceptions last -> Option A

4. Quick Check:

   Specific before general catch blocks [OK]

Hint: Put specific exceptions before general ones in catch blocks [OK]

Common Mistakes:

• Placing general catch before specific causes unreachable code
• Assuming catch order does not matter
• Trying to use multiple catch blocks without try

3.

What will be the output of this C# code?

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

medium

A. No output, program crashes

B. General error caught

C. Index error caught

D. Compilation error

Solution

1. Step 1: Identify the exception thrown

   Accessing arr[5] causes an IndexOutOfRangeException because the array size is 2.

2. Step 2: Match exception to catch block

   The first catch block matches IndexOutOfRangeException, so it runs and prints "Index error caught".

3. Final Answer:

   Index error caught -> Option C

4. Quick Check:

   IndexOutOfRangeException triggers first catch [OK]

Hint: Exception type matches first suitable catch block [OK]

Common Mistakes:

• Thinking general catch runs before specific
• Assuming no exception occurs
• Confusing exception types

4.

Find the error in this code snippet:

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

medium

A. The FormatException catch block is unreachable

B. Missing finally block

C. Try block syntax is incorrect

D. No error, code is correct

Solution

1. Step 1: Check catch block order

   The first catch block catches all Exception types, including FormatException.

2. Step 2: Identify unreachable catch block

   Since Exception catch is first, the FormatException catch block can never run, causing a compile error.

3. Final Answer:

   The FormatException catch block is unreachable -> Option A

4. Quick Check:

   General catch before specific causes unreachable code [OK]

Hint: Place specific catch blocks before general ones to avoid unreachable code [OK]

Common Mistakes:

• Putting general catch before specific
• Ignoring unreachable code errors
• Thinking finally block is mandatory

5.

You want to handle NullReferenceException and DivideByZeroException differently, but also catch any other exceptions generally. Which is the best order of catch blocks?

try {
    // code that may throw exceptions
} catch (___) {
    Console.WriteLine("Null reference error");
} catch (___) {
    Console.WriteLine("Divide by zero error");
} catch (___) {
    Console.WriteLine("Other error");
}

hard

A. Exception, DivideByZeroException, NullReferenceException

B. Exception, NullReferenceException, DivideByZeroException

C. DivideByZeroException, Exception, NullReferenceException

D. NullReferenceException, DivideByZeroException, Exception

Solution

1. Step 1: Identify specific exceptions

   NullReferenceException and DivideByZeroException are specific exceptions to catch first.

2. Step 2: Place general exception last

   The general Exception catch block should come last to catch all other exceptions.

3. Final Answer:

   NullReferenceException, DivideByZeroException, Exception -> Option D

4. Quick Check:

   Specific exceptions first, general last [OK]

Hint: Catch specific exceptions before general Exception last [OK]

Common Mistakes:

• Putting Exception catch first
• Mixing order of specific exceptions
• Omitting general catch block