Exception handling flow in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to throw an exception of type int.

C++

#include <iostream>

int main() {
    try {
        throw [1];
    } catch (int e) {
        std::cout << "Caught exception: " << e << std::endl;
    }
    return 0;
}

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

A5

B"error"

C3.14

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Throwing a string or other type that does not match the catch block.

Forgetting to use throw keyword.

The throw statement throws an exception. Here, 5 is an int, matching the catch (int e) block.

2fill in blank

medium

Complete the code to catch exceptions of type std::string.

C++

#include <iostream>
#include <string>

int main() {
    try {
        throw std::string("error");
    } catch ([1] e) {
        std::cout << "Caught string exception: " << e << std::endl;
    }
    return 0;
}

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

Achar

Bint

Cdouble

Dstd::string&

Attempts:

3 left

💡 Hint

Common Mistakes

Catching by value or wrong type causing no catch.

Using primitive types instead of std::string.

The catch block must match the thrown exception type. Here, std::string& catches the thrown std::string by reference.

3fill in blank

hard

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

C++

#include <iostream>

int main() {
    try {
        throw 1.23;
    } catch ([1]) {
        std::cout << "Caught an exception" << std::endl;
    }
    return 0;
}

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

Aint e

Bdouble e

C...

Dchar e

Attempts:

3 left

💡 Hint

Common Mistakes

Specifying a wrong type in catch causing uncaught exceptions.

Missing catch block for thrown type.

The catch(...) block catches any exception regardless of type.

4fill in blank

hard

Fill both blanks to throw and catch a const char* exception.

C++

#include <iostream>

int main() {
    try {
        throw [1];
    } catch ([2] e) {
        std::cout << "Caught message: " << e << std::endl;
    }
    return 0;
}

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

A"error occurred"

Bint

Cconst char*

Ddouble

Attempts:

3 left

💡 Hint

Common Mistakes

Throwing a string literal but catching as std::string.

Mismatched catch type causing uncaught exception.

The thrown exception is a string literal which is of type const char*. The catch block must match this type.

5fill in blank

hard

Fill all three blanks to create a map of exception types to messages using a lambda.

C++

#include <iostream>
#include <map>
#include <string>

int main() {
    std::map<std::string, std::string> errorMessages = {
        {"int", "Integer error"},
        {"double", "Double error"},
        {"string", "String error"}
    };

    auto getMessage = [&](const std::string& type) -> std::string {
        if (errorMessages.find([1]) != errorMessages.end()) {
            return errorMessages[[2]];
        } else {
            return [3];
        }
    };

    std::cout << getMessage("int") << std::endl;
    std::cout << getMessage("bool") << std::endl;

    return 0;
}

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

Atype

C"Unknown error"

D"No error"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names inside the lambda.

Returning wrong default message.

The lambda checks if the type exists in the map. If yes, it returns the corresponding message; otherwise, it returns "Unknown error".

Practice

1. What is the main purpose of using try and catch blocks in C++?

easy

A. To speed up the program execution

B. To handle errors and keep the program running smoothly

C. To declare variables

D. To create loops

Solution

1. Step 1: Understand the role of try block

   The try block contains code that might cause errors or exceptions during execution.

2. Step 2: Understand the role of catch block

   The catch block handles those errors so the program does not crash and can continue running.

3. Final Answer:

   To handle errors and keep the program running smoothly -> Option B

4. Quick Check:

   Exception handling = handle errors safely [OK]

Hint: Try-catch blocks catch errors to avoid crashes [OK]

Common Mistakes:

• Thinking try-catch speeds up code
• Confusing try-catch with loops
• Using try-catch to declare variables

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

easy

A. catch (int e) { /* handle error */ }

B. catch int (e) { /* handle error */ }

C. catch { int e; /* handle error */ }

D. catch (e int) { /* handle error */ }

Solution

1. Step 1: Recall correct catch syntax

   The catch block must specify the exception type in parentheses followed by a variable name, like catch (int e).

2. Step 2: Identify syntax errors in other options

   The other options contain syntax errors such as reversed type and variable order, incorrect keyword placement, or missing parentheses with improper declaration.

3. Final Answer:

   catch (int e) { /* handle error */ } -> Option A

4. Quick Check:

   Correct catch syntax = catch (type var) [OK]

Hint: Catch syntax: catch (type variable) { } [OK]

Common Mistakes:

• Omitting parentheses in catch
• Swapping type and variable order
• Missing variable name in catch

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

try {
  throw 5;
  std::cout << "No Exception" << std::endl;
} catch (int e) {
  std::cout << "Caught exception: " << e << std::endl;
}

medium

A. Program crashes

B. No Exception

C. Caught exception: 5

D. No output

Solution

1. Step 1: Understand the throw statement

   The code throws an integer exception with value 5, so control jumps to the catch block immediately.

2. Step 2: Identify which catch block runs

   The catch block for int e catches the exception and prints the message with the value 5.

3. Final Answer:

   Caught exception: 5 -> Option C

4. Quick Check:

   Throw 5 caught by catch(int) = output message [OK]

Hint: Throw jumps to matching catch, skipping rest of try [OK]

Common Mistakes:

• Expecting code after throw to run
• Thinking program crashes without catch
• Ignoring exception value in output

4. Identify the error in this code snippet:

try {
  int x = 10 / 0;
} catch (double e) {
  std::cout << "Caught double exception" << std::endl;
}

medium

A. Division by zero causes a runtime error but no exception is thrown

B. Catch block should catch int, not double

C. Try block syntax is incorrect

D. No error, code runs fine

Solution

1. Step 1: Analyze division by zero in C++

   Integer division by zero causes undefined behavior or runtime error but does not throw a C++ exception automatically.

2. Step 2: Check catch block type

   The catch block expects a double exception, but no exception is thrown, so it never runs.

3. Final Answer:

   Division by zero causes a runtime error but no exception is thrown -> Option A

4. Quick Check:

   Integer divide by zero = runtime error, no catch [OK]

Hint: Integer divide by zero crashes, no catch thrown [OK]

Common Mistakes:

• Assuming division by zero throws exception
• Mismatching catch type with thrown exception
• Thinking try block syntax is wrong

5. Given this code, what will be the output?

try {
  try {
    throw std::string("Error");
  } catch (int e) {
    std::cout << "Caught int" << std::endl;
  }
} catch (std::string &e) {
  std::cout << "Caught string: " << e << std::endl;
}

hard

A. Caught int

B. Program crashes

C. No output

D. Caught string: Error

Solution

1. Step 1: Trace inner try-catch

   The inner try throws a std::string exception. The inner catch expects int, so it does not catch this exception.

2. Step 2: Trace outer catch block

   The exception propagates to the outer catch, which catches std::string &e and prints the message.

3. Final Answer:

   Caught string: Error -> Option D

4. Quick Check:

   Inner catch mismatch, outer catch handles string [OK]

Hint: Exception bubbles up until matching catch found [OK]

Common Mistakes:

• Assuming inner catch catches all exceptions
• Ignoring exception propagation
• Expecting program crash on uncaught inner exception