Question

Consider the following \(\mathrm{C}++\) code: double balance; try { cout << "Enter the balance: "; cin >> balance; cout << endl; if (balance < 1000.00) throw balance; cout << "Leaving the try block." << endl; } catch (double x) { cout << "Current balance: " << x << endl << "Balance must be greater than 1000.00" << endl; } a. In this code, identify the try block. b. In this code, identify the catch block. c. In this code, identify the catch block parameter and its type. d. In this code, identify the throw statement.

Short answer

a. Try block: lines from "try {" to before "catch". b. Catch block: lines from "catch (double x) {" to "}". c. Catch block parameter: x, Type: double. d. Throw statement: "throw balance;".

Step-by-step solution

Identify the Try Block

The "try block" in the code is the portion contained within the braces following the "try" keyword. In this case, it starts after "try {" and ends before the corresponding "catch" block begins. It includes the following statements: 1. Requesting the user to enter a balance. 2. Reading the entered balance into the variable 'balance'. 3. Checking if the balance is less than 1000.00, and if so, throwing an exception.

Identify the Catch Block

The "catch block" immediately follows the "try" block and is indicated by the keyword "catch". It begins after "catch (double x) {" and ends with the corresponding closing brace "}", containing the code to handle the exception. In this code, the catch block outputs the current balance and informs that the balance must be greater than 1000.00.

Identify the Catch Block Parameter and Type

In the catch block, the parameter is presented in the parentheses following the "catch" keyword. For this code, the catch block is specified as "catch (double x)", where "x" is the parameter and "double" is its type. It is meant to catch exceptions of type 'double', representing the thrown balance value.

Identify the Throw Statement

The "throw statement" is used within the "try block" to signal an exception when a specific condition is met. In this code, the throw statement is executed when "balance < 1000.00" evaluates to true. It appears as "throw balance;", indicating that the current value of 'balance' is thrown as an exception.

Key concepts

Try Block

In C++, the "try block" is used to test a piece of code for errors. This block is essential for managing exceptions, meaning unexpected events that disrupt normal program flow. The try block starts with the keyword "try" followed by curly braces `{}` that enclose the statements to be tested.
In the provided code, the try block prompts the user to enter a balance, reads the user's input, and checks if the entered balance is below a specified threshold of 1000.00. If this condition is met, the block throws an exception to signal this unusual situation. Hence, the actions included in this try block are:

• Requesting and receiving input for the balance.
• Checking if the balance is below the limit.
• Executing the throw statement if the condition is met.

Catch Block

The "catch block" in C++ is designed to handle exceptions thrown by the try block. It immediately follows the try block and begins with the keyword "catch". This block is where you define corrective actions for the exceptions, allowing the program to recover or inform the user about the error rather than crashing.
Inside the catch block of the provided code, when an exception (i.e., a balance less than 1000.00) is thrown, it displays the erroneous balance to the user and provides a message indicating the minimum required balance. Here is an outline of its duties:

• Capturing the thrown exception value.
• Displaying the exception value (the balance).
• Informing the user of the correct requirement (balance must exceed 1000.00).

This ensures the program gracefully alerts users to the issue, maintaining stability and user comprehension.

Throw Statement

The "throw statement" in C++ is a crucial part of exception handling, located inside the try block. It is used to signal the occurrence of an exceptional condition, kicking off the error-handling process.
In the code example given, the throw statement is triggered if the balance entered is less than 1000.00. The syntax `throw balance;` indicates that the current balance value, which failed the check, is passed as an exception.
When this statement executes, the normal flow of the program is interrupted, and control is transferred to the corresponding catch block. This ensures that program execution can be directed to handle errors specifically where they occur rather than leading to undefined behavior.

Catch Block Parameter

The "catch block parameter" is used in a catch block to receive any exception values thrown by the try block. It acts as a placeholder for the exception data so that the catch block can process it accordingly.
In the code presented, `catch (double x)` includes the parameter `x`, of type `double`. This parameter "x" is effectively a local variable within the catch block. It holds the value of the thrown double-type exception, which in this context is the balance amount that was less than 1000.00.
Understanding the catch block parameter's role is essential because it directly links the thrown exception to the corrective actions specified in the catch block. This mechanism enables programmers to write robust code that handles different types of exceptions logically and systematically.