Try–catch block in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of try–catch with integer exception

What is the output of this C++ code?

C++

#include <iostream>

int main() {
    try {
        throw 5;
    } catch (int e) {
        std::cout << "Caught integer: " << e << std::endl;
    }
    return 0;
}

A Caught integer: 0

B Caught integer: 5

C No output

D Compilation error

💡 Hint

The throw statement throws an integer, which is caught by the catch block.

The try block throws an integer 5. The catch block catches an int and prints it.

❓ Predict Output

intermediate

Output when no exception is thrown

What will this C++ program output?

C++

#include <iostream>

int main() {
    try {
        std::cout << "Inside try block" << std::endl;
    } catch (...) {
        std::cout << "Caught exception" << std::endl;
    }
    std::cout << "After try-catch" << std::endl;
    return 0;
}

A

Inside try block
After try-catch

B Compilation error

C Inside try block

D

Caught exception
After try-catch

💡 Hint

No exception is thrown, so catch block is skipped.

Since no exception is thrown, the catch block is not executed. Both print statements run.

❓ Predict Output

advanced

Output with multiple catch blocks

What is the output of this C++ code?

C++

#include <iostream>

int main() {
    try {
        throw 'a';
    } catch (int e) {
        std::cout << "Caught int: " << e << std::endl;
    } catch (char e) {
        std::cout << "Caught char: " << e << std::endl;
    } catch (...) {
        std::cout << "Caught unknown exception" << std::endl;
    }
    return 0;
}

A Compilation error

B Caught int: 97

C Caught unknown exception

D Caught char: a

💡 Hint

The thrown type is char, so the matching catch block runs.

The throw statement throws a char 'a'. The catch block for char catches it and prints it.

❓ Predict Output

advanced

Exception not caught by specific catch block

What happens when this C++ code runs?

C++

#include <iostream>

int main() {
    try {
        throw 3.14;
    } catch (int e) {
        std::cout << "Caught int: " << e << std::endl;
    }
    return 0;
}

A Program terminates with uncaught exception

B Caught int: 3

C Caught int: 3.14

D Compilation error

💡 Hint

The thrown type is double but catch expects int.

The thrown double 3.14 is not caught by catch(int), so the exception is uncaught and program terminates.

🧠 Conceptual

expert

Behavior of nested try–catch blocks

Consider this C++ code with nested try–catch blocks. What is the output?

C++

#include <iostream>

int main() {
    try {
        try {
            throw 10;
        } catch (double e) {
            std::cout << "Inner catch double" << std::endl;
        }
    } catch (int e) {
        std::cout << "Outer catch int: " << e << std::endl;
    }
    return 0;
}

A No output

B Inner catch double

C Outer catch int: 10

D Compilation error

💡 Hint

The inner catch does not catch int, so exception propagates to outer catch.

The inner try throws int 10, inner catch expects double so it does not catch. Exception goes to outer catch which catches int and prints it.

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