Question

Write \(\mathrm{C}++\) statements that do the following: a. Define an enum type, bookType, with the values MATH, CSC, ENGLISH, HISTORY, PHYSICS, and PHILOSOPHY. b. Declare a variable book of type bookType. c. Assign MATH to the variable book. d. Advance book to the next value in the list. e. Output the value of the variable book.

Short answer

Define an enum, declare and assign a value, increment it, then print it.

Step-by-step solution

Define the Enum

Define an enum type called `bookType` with the specified book categories as values. In C++, this is done using the `enum` keyword followed by the desired enumeration name and the list of values. ```cpp enum bookType { MATH, CSC, ENGLISH, HISTORY, PHYSICS, PHILOSOPHY }; ```

Declare the Enum Variable

Declare a variable named `book` of the enum type `bookType`. This variable will be used to hold one of the values from the defined enum. ```cpp bookType book; ```

Assign a Value to the Enum Variable

Assign the value `MATH` to the `book` variable. Since `MATH` is a valid value of `bookType`, the assignment is straightforward. ```cpp book = MATH; ```

Advance the Enum Variable

To advance the value of `book` from `MATH` to the next value in the enum list, increment the variable `book`. This works because the enum values are implicitly converted to integers starting from 0. ```cpp book = static_cast(book + 1); ```

Output the Enum Variable

Display the current value of the `book` variable. Since `book` is of an enum type, we need to cast it to an integer to view its corresponding integer value, or use a custom function to map back to strings if necessary in real applications. ```cpp std::cout << book << std::endl; // Outputs 1, which corresponds to CSC if using default enum indexing. ```

Key concepts

Understanding Enumeration in C++

In C++, an `enum` (short for enumeration) is a user-defined data type that consists of integral constants. It's essentially a way to assign names to numbers, making programs more readable. For example, in a list of book categories, instead of using numbers, we can define meaningful names using an enum. Here is how you can define an enum:

• `enum bookType { MATH, CSC, ENGLISH, HISTORY, PHYSICS, PHILOSOPHY };`

When you define an `enum`, the compiler assigns integer values to each of the names starting from 0. Thus, `MATH` will be 0, `CSC` will be 1, and so on.
The enum helps manage constants that are related, allowing your code to be cleaner and more maintainable.

Using enums can prevent magic numbers, improving the robustness of your code by making it more understandable and less error-prone.

The Role of Variable Declaration

Declaring variables, especially for an enum in C++, is quite similar to declaring other types of variables. Once you have your enum type defined, you can declare a variable of that type to store a value from the enum.

Here's the syntax for declaring a variable `book` of type `bookType`:

• `bookType book;`

This line of code prepares a container `book` in memory, specifically to hold any of the predefined values like `MATH` or `CSC` from the `bookType` enumeration.

The declared variable will be type-safe to only allow values within its defined enumeration, hence reducing possible errors by constrained assignment of invalid values.

How to Increment Enum Values

Enum values in C++ can be incremented similar to integer values, thanks to their underlying integer representation. The ability to increment an enum value is particularly useful when you want to cycle through the enum values logically. The code snippet for incrementing an enum value looks like this:

• `book = static_cast(book + 1);`

What this does is: it retrieves the integer value of the `book` (currently `MATH`, which is 0), adds one to it to move to the next value, and then uses `static_cast` to convert back to the `bookType` before assigning.

This approach ensures type safety, allowing you to maintain control over correct value transitions within the enum. However, care must be taken as blindly incrementing can lead to exceeding the defined enum values, requiring additional checks to keep within bounds.