Try–catch block in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to catch an exception thrown inside the try block.

C++

try {
    throw std::runtime_error("Error occurred");
} catch ([1]) {
    std::cout << "Exception caught" << std::endl;
}

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

Aconst std::exception& e

Bint e

Cdouble e

Dchar e

Attempts:

3 left

💡 Hint

Common Mistakes

Catching exceptions by value instead of by reference.

Using incorrect exception types like int or char.

The catch block should catch exceptions by reference to std::exception or its derived classes to handle standard exceptions properly.

2fill in blank

medium

Complete the code to throw a standard exception with a message.

C++

void test() {
    [1] std::runtime_error("Something went wrong");
}

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

Athrow

Bcatch

Ctry

Dreturn

Attempts:

3 left

💡 Hint

Common Mistakes

Using try or catch instead of throw.

Forgetting to throw the exception object.

The throw keyword is used to raise an exception in C++.

3fill in blank

hard

Fix the error in the catch block to properly catch all exceptions.

C++

try {
    // some code
} catch ([1]) {
    std::cout << "Caught an exception" << std::endl;
}

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

Aint e

Bstd::exception e

Cchar e

D...

Attempts:

3 left

💡 Hint

Common Mistakes

Catching exceptions by value instead of reference.

Not catching all exception types.

Using ... in catch block catches all exceptions regardless of type.

4fill in blank

hard

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

C++

try {
    throw std::runtime_error("Error");
} catch ([1]) {
    std::cout << e.[2]() << std::endl;
}

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

Aconst std::exception& e

Bwhat

Cmessage

Dconst char* e

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect exception types.

Trying to access a non-existent method like message().

Catch the exception by reference and use the what() method to get the error message.

5fill in blank

hard

Fill all three blanks to throw and catch a custom exception with a message.

C++

class MyException : public std::exception {
public:
    const char* [1]() const noexcept override {
        return "Custom error";
    }
};

int main() {
    try {
        [2] MyException();
    } catch ([3]) {
        std::cout << e.what() << std::endl;
    }
    return 0;
}

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

Awhat

Bthrow

Cconst MyException& e

Dcatch

Attempts:

3 left

💡 Hint

Common Mistakes

Not overriding what() correctly.

Catching exceptions by value instead of reference.

Using catch keyword incorrectly.

The method what() returns the error message. Use throw to raise the exception and catch it by reference.

Practice

1.

What is the main purpose of a try-catch block in C++?

easy

A. To handle errors and exceptions safely during program execution

B. To speed up the program by skipping code

C. To declare variables globally

D. To create loops that run multiple times

Solution

1. Step 1: Understand the role of try block

   The try block contains code that might cause an error or exception.

2. Step 2: Understand the role of catch block

   The catch block handles the error so the program does not crash.

3. Final Answer:

   To handle errors and exceptions safely during program execution -> Option A

4. Quick Check:

   Try-catch handles errors = B [OK]

Hint: Try-catch blocks catch errors to keep programs running [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 start a try block in C++?

?

easy

A. catch {

B. try (

C. try:

D. try {

Solution

1. Step 1: Recall try block syntax

   The try block starts with the keyword try followed by curly braces { }.

2. Step 2: Identify correct option

   Only try { uses try { which is correct syntax to start the block.

3. Final Answer:

   try { -> Option D

4. Quick Check:

   Try block starts with try { = C [OK]

Hint: Try block always starts with 'try {' in C++ [OK]

Common Mistakes:

• Using parentheses instead of curly braces
• Starting with catch instead of try
• Using colon after try

3.

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

try {
    int x = 5 / 0;
    std::cout << "Result: " << x << std::endl;
} catch (const std::exception& e) {
    std::cout << "Caught exception" << std::endl;
}

medium

A. Result: 0

B. Caught exception

C. Program crashes with division by zero error

D. No output

Solution

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

   Integer division by zero causes undefined behavior and usually crashes the program; it does not throw a standard exception.

2. Step 2: Check catch block type

   The catch block catches std::exception types, but division by zero does not throw this exception automatically.

3. Final Answer:

   Program crashes with division by zero error -> Option C

4. Quick Check:

   Integer division by zero crashes = D [OK]

Hint: Division by zero crashes, not caught by std::exception [OK]

Common Mistakes:

• Assuming catch block catches all errors
• Expecting output 'Caught exception'
• Thinking division by zero returns zero

4.

Identify the error in this C++ code snippet:

try {
    throw 10;
} catch (int e) {
    std::cout << "Caught int: " << e << std::endl;
} catch (...) {
    std::cout << "Caught unknown" << std::endl;
}

medium

A. The catch block for int should come after catch(...)

B. No error; code is correct

C. Multiple catch blocks are not allowed

D. Throwing int is invalid

Solution

1. Step 1: Check throw and catch types

   The code throws an int and catches it with catch(int e), which matches correctly.

2. Step 2: Verify catch block order

   The specific catch catch(int e) comes before the catch-all catch(...), which is correct.

3. Final Answer:

   No error; code is correct -> Option B

4. Quick Check:

   Throw int caught by int catch first = A [OK]

Hint: Specific catch blocks must come before catch(...) [OK]

Common Mistakes:

• Placing catch(...) before specific catch
• Thinking multiple catch blocks are invalid
• Believing throwing int is not allowed

5.

Consider this code snippet:

try {
    std::string s = "hello";
    int n = std::stoi(s);
    std::cout << n << std::endl;
} catch (const std::invalid_argument& e) {
    std::cout << "Invalid argument caught" << std::endl;
} catch (...) {
    std::cout << "Other exception caught" << std::endl;
}

What will be the output and why?

hard

A. Invalid argument caught

B. Other exception caught

C. hello

D. Program crashes

Solution

1. Step 1: Understand std::stoi behavior

   Trying to convert "hello" to int using std::stoi throws std::invalid_argument exception because "hello" is not a number.

2. Step 2: Check catch blocks

   The first catch block catches std::invalid_argument exceptions and prints "Invalid argument caught".

3. Final Answer:

   Invalid argument caught -> Option A

4. Quick Check:

   std::stoi throws invalid_argument for non-numeric string = A [OK]

Hint: std::stoi throws invalid_argument on bad input [OK]

Common Mistakes:

• Expecting program to print 'hello'
• Assuming catch(...) runs instead of specific catch
• Thinking program crashes without catch