Try–catch block in C++ - Mini Project: Build & Apply

Handling Errors with Try-Catch Block in C++

📖 Scenario: Imagine you are building a simple calculator program that divides two numbers. Sometimes, the user might enter zero as the divisor, which causes an error. We want to handle this error gracefully so the program does not crash.

🎯 Goal: You will create a program that uses a try-catch block to catch division by zero errors and display a friendly message instead of crashing.

📋 What You'll Learn

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

Create a boolean variable named error_occurred and set it to false.

Use a try block to perform the division numerator / denominator and store the result in an integer variable named result.

Use a catch block to catch a std::exception and set error_occurred to true.

Print "Error: Division by zero is not allowed." if error_occurred is true, otherwise print the division result.

💡 Why This Matters

🌍 Real World

Try-catch blocks are used in real programs to handle unexpected errors like file not found, network problems, or invalid user input without crashing.

💼 Career

Understanding error handling is important for writing reliable software and is a common requirement in programming jobs.

1

Create variables for division

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 error flag variable

Create a boolean variable called error_occurred and set it to false.

C++

int numerator = 10;
int denominator = 0;
# Your code here

Hint

Use bool error_occurred = false; to create the flag variable.

3

Use try-catch block for division

Write a try block that divides numerator by denominator and stores the result in an integer variable called result. Then write a catch block that catches std::exception& and sets error_occurred to true.

C++

int numerator = 10;
int denominator = 0;
bool error_occurred = false;
# Your code here

Hint

Use try { ... } and catch (const std::exception& e) { ... }. Throw an exception if denominator is zero.

4

Print the result or error message

Write an if statement that checks if error_occurred is true. If yes, print "Error: Division by zero is not allowed.". Otherwise, print the division result stored in result. Note: Declare result before the try block so it is accessible.

C++

int numerator = 10;
int denominator = 0;
bool error_occurred = false;

# Your code here

Hint

Use if (error_occurred) { std::cout << ... } else print the result.

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