Multiple catch blocks in C++ - Mini Project: Build & Apply

Handling Multiple Exceptions with Multiple Catch Blocks in C++

📖 Scenario: Imagine you are writing a simple program that divides two numbers. Sometimes, the user might enter zero as the divisor, which causes an error. Other times, the user might enter a non-number, causing a different error. You want to catch these errors separately and show clear messages.

🎯 Goal: You will create a program that uses try and catch blocks to handle different types of errors separately. This will help the program respond correctly to different problems.

📋 What You'll Learn

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

Create a try block where you check if denominator is zero and throw an int exception with value 0 if true.

Add a catch block to catch the int exception and print "Error: Division by zero!".

Add another catch block to catch any other exceptions of type const char* and print "Error: Invalid input!".

💡 Why This Matters

🌍 Real World

Handling errors properly is important in real-world programs to avoid crashes and to give users clear feedback when something goes wrong.

💼 Career

Knowing how to use multiple catch blocks is a key skill for software developers to write safe and reliable C++ applications.

1

Create the initial variables

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

C++

// Your code here

Hint

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

2

Add the try block with exception throwing

Add a try block. Inside it, check if denominator is zero. If yes, throw an int exception with value 0. Otherwise, calculate numerator / denominator and store it in an integer variable called result.

C++

int numerator = 10;
int denominator = 0;

// Add try block and throw exception if denominator is zero
// Your code here

Hint

Use try { ... } and inside it use if (denominator == 0) throw 0;.

3

Add multiple catch blocks

Add two catch blocks after the try block. The first catch block should catch an int exception and print "Error: Division by zero!". The second catch block should catch a const char* exception and print "Error: Invalid input!".

C++

int numerator = 10;
int denominator = 0;

try {
    if (denominator == 0) {
        throw 0;
    }
    int result = numerator / denominator;
}
// Add two catch blocks here
// Your code here

Hint

Use catch (int) { ... } and catch (const char*) { ... } blocks with std::cout to print messages.

4

Print the final output

Add a main function around your code and include #include <iostream>. Run the program to see the output. The program should print Error: Division by zero!.

C++

#include 

// Wrap the code in main function and run
// Your code here

Hint

Make sure to include #include <iostream> and wrap your code inside int main() { ... }. Use std::cout to print the messages.

Practice

1.

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

easy

A. To speed up the program execution

B. To handle different types of exceptions separately

C. To avoid using try blocks

D. To declare multiple variables at once

Solution

1. Step 1: Understand the role of catch blocks

   Catch blocks are used to handle exceptions that occur in the try block.

2. Step 2: Recognize the benefit of multiple catch blocks

   Multiple catch blocks allow handling different exception types separately, so each error can be managed properly.

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
• Confusing catch blocks with variable declarations
• Believing try blocks are not needed with multiple catch blocks

2.

Which of the following is the correct syntax to catch any remaining exceptions in multiple catch blocks in C++?

try {
    // code
}
catch (int e) {
    // handle int
}
_____ {
    // handle other
}

easy

A. catch (...)

B. catch (string e)

C. catch (double e)

D. catch (char e)

Solution

1. Step 1: Identify the syntax for catch-all block

   The catch(...) block catches any exception type not caught by previous catch blocks.

2. Step 2: Confirm correct syntax

   Only catch(...) uses ellipsis and no variable type, making it the correct syntax for a generic catch block.

3. Final Answer:

   catch (...) -> Option A

4. Quick Check:

   catch(...) = catch all exceptions [OK]

Hint: Use catch(...) to catch all exceptions generically [OK]

Common Mistakes:

• Using catch without parentheses
• Trying to catch unknown types without ellipsis
• Misplacing catch blocks after try

3.

What will be the output of the following C++ code?

try {
    throw 10;
}
catch (double e) {
    std::cout << "Double exception";
}
catch (int e) {
    std::cout << "Integer exception: " << e;
}

medium

A. Compilation error

B. Double exception

C. No output

D. Integer exception: 10

Solution

1. Step 1: Identify the thrown exception type

   The code throws an integer exception with value 10.

2. Step 2: Match thrown exception with catch blocks

   The first catch block expects a double, so it is skipped. The second catch block matches int, so it executes and prints the message.

3. Final Answer:

   Integer exception: 10 -> Option D

4. Quick Check:

   throw int = catch int block runs [OK]

Hint: Match thrown type with catch parameter type [OK]

Common Mistakes:

• Assuming first catch always runs
• Confusing int and double types
• Expecting no output if types differ

4.

Find the error in this code snippet using multiple catch blocks:

try {
    throw "error";
}
catch (int e) {
    std::cout << "Int error";
}
catch (char e) {
    std::cout << "Char error";
}

medium

A. Missing catch block for const char* exception

B. Try block syntax is incorrect

C. Cannot throw string literals

D. Catch blocks must be in reverse order

Solution

1. Step 1: Identify the thrown exception type

   The code throws a string literal, which is of type const char*.

2. Step 2: Check catch blocks for matching types

   Catch blocks handle int and char, but not const char*. So no catch block matches the thrown exception, causing an unhandled exception.

3. Final Answer:

   Missing catch block for const char* exception -> Option A

4. Quick Check:

   Thrown type must match catch parameter [OK]

Hint: Catch blocks must match thrown exception types exactly [OK]

Common Mistakes:

• Assuming char catch handles string literals
• Thinking try block syntax is wrong
• Believing catch order matters for unrelated types

5.

Consider this code with multiple catch blocks:

try {
    throw std::runtime_error("runtime error");
}
catch (std::exception& e) {
    std::cout << "Exception: " << e.what();
}
catch (std::runtime_error& e) {
    std::cout << "Runtime error: " << e.what();
}

What will be the output and why?

hard

A. Exception: runtime error

B. Runtime error: runtime error

C. Compilation error due to catch order

D. No output because exception is not caught

Solution

1. Step 1: Understand exception inheritance

   std::runtime_error is derived from std::exception, so it matches both catch blocks.

2. Step 2: Analyze catch block order

   The first catch block catches std::exception by reference, so it catches the thrown runtime_error before the second catch block is reached.

3. Step 3: Determine output

   The first catch block prints "Exception: runtime error" using e.what().

4. Final Answer:

   Compilation error due to catch order -> Option C

5. Quick Check:

   Derived class catch must come before base class catch to avoid compilation error [OK]

Hint: Catch derived exceptions before base to avoid compilation error [OK]

Common Mistakes:

• Expecting derived catch to run first
• Thinking catch order causes no compilation error
• Assuming no output if multiple matches