Question

Consider the following \(\mathrm{C}++\) code: int lowerLimit; int divisor; int result; try { cout << "Entering the try block." << endl; if (divisor == 0) throw 0; if (lowerLimit < 100) throw string("Lower limit violation."); result = lowerLimit / divisor; cout << "Exiting the try block." << endl; } catch (int x) { cout << "Exception: " << x << endl; result = 120; } catch (string str) { cout << "Exception: " << str << endl; } cout << "After the catch block" << endl; What is the output if: a. The value of lowerLimit is \(50,\) and the value of divisor is \(10 ?\) b. The value of lowerLimit is \(50,\) and the value of divisor is \(0 ?\) c. The value of lowerLimit is \(150,\) and the value of divisor is \(10 ?\) d. The value of lowerLimit is \(150,\) and the value of divisor is 0 ?

Short answer

a: "Exception: Lower limit violation." b: "Exception: 0" c: "Exiting the try block." d: "Exception: 0"

Step-by-step solution

Understanding the Try Block

The code is structured with a try-catch block to handle exceptions. The key points in the try block are: 1. If `divisor == 0`, an integer exception is thrown. 2. If `lowerLimit < 100`, a string exception is thrown. 3. If no exception is thrown, `result` is calculated as `lowerLimit / divisor`, and a message is printed to indicate the try block is exited.

Analyzing Catch Blocks

There are two catch blocks: 1. The first catch block handles an integer exception, setting `result` to 120 and displaying an exception message. 2. The second catch block handles a string exception, printing out the exception message. After any exception is caught and handled, the program outputs "After the catch block".

Case a: lowerLimit = 50, divisor = 10

1. Entering the try block, neither the `divisor == 0` nor `lowerLimit < 100` conditions are true. 2. The condition `lowerLimit < 100` is true, so it throws a string exception with the message "Lower limit violation." 3. The string exception is caught in the second catch block, displaying "Exception: Lower limit violation." 4. Finally, "After the catch block" is printed.

Case b: lowerLimit = 50, divisor = 0

1. The try block starts, and the condition `divisor == 0` is true. 2. An integer exception is thrown with the value `0`. 3. The integer exception is caught by the first catch block, setting `result` to 120 and displaying "Exception: 0." 4. "After the catch block" is printed.

Case c: lowerLimit = 150, divisor = 10

1. Entering the try block, neither exception condition is met since `divisor` is not zero and `lowerLimit` is not less than 100. 2. The program calculates `result = 150 / 10 = 15`. 3. "Exiting the try block." is printed, indicating no exceptions were thrown. 4. Finally, "After the catch block" is printed.

Case d: lowerLimit = 150, divisor = 0

1. Start the try block. The condition `divisor == 0` is true. 2. An integer exception (0) is thrown and caught by the first catch block. 3. The catch block sets `result` to 120 and prints "Exception: 0." 4. "After the catch block" is displayed as the final message.

Key concepts

try-catch blocks

In C++, the try-catch block is a fundamental construct for handling exceptions. Essentially, it allows you to isolate the code that might throw an exception and provide specific handling for different types of exceptions. The "try" block encloses the code that is to be "tested" for errors or exceptions. If the code executes without any issues, the program continues past the "catch" blocks. However, if an exception occurs, the program will jump from the "try" block to the appropriate "catch" block.
A "catch" block follows the "try" block and is used to catch and handle the exceptions thrown within the "try" block. You can have multiple "catch" blocks, each tailored to handle different types of exceptions. The variety in the kinds of exceptions that can be handled makes this construct very powerful. It ensures the program doesn’t crash but rather handles errors gracefully by providing meaningful messages or alternative actions.

integer exceptions

In C++, integer exceptions are used to handle errors that involve integers, such as dividing by zero. In the provided code, an integer exception is explicitly thrown when the divisor is zero using the statement `throw 0;`. This type of exception is particularly critical when dealing with arithmetic operations where division is involved.
These exceptions are handled by catch blocks that specify `catch (int x)` where `x` is the integer that was thrown. When this block is executed, we can provide a customized response by interpreting the integer value, which acts as an error code. For instance, in the example code, the integer exception causes the program to set a default result value and print a corresponding error message. This allows the program to continue operating in a controlled manner even after an error occurs.

string exceptions

String exceptions in C++ provide a mechanism for handling errors by throwing a string, typically an error message. This technique is demonstrated in the code when a condition violation occurs, such as when `lowerLimit < 100`. At this point, a string exception is thrown with a message like `throw string("Lower limit violation.");`.
The string passed with the exception serves to provide a human-readable description of the error, which can be very helpful for debugging and user communication. In our example, if this exception is thrown, it gets caught in the corresponding `catch (string str)` block, where `str` is the string that was thrown. The program can then print the error message or take another remedial action. By using string exceptions, you can ensure that your error handling provides clear and specific information, which makes debugging and maintaining programs much easier.

division by zero handling

Handling division by zero is one of the most common and important tasks when programming arithmetic operations. In C++, dividing by zero typically leads to undefined behavior and can cause the program to crash. In the example code given, this is precisely managed by using a "try-catch" block to prevent the program from crashing.
When the `divisor` is zero, a division by zero situation arises, which would cause an integer exception to be thrown using the statement `throw 0;`. The "catch" block specifically designed for integer exceptions handles this error by setting a standard result value and displaying an informative message. This practice of prior checking and handling division by zero is crucial in applications that involve calculator functions or any computation where division can occur. It ensures that the program runs smoothly and continues execution even after encountering such an illegal operation.