Question

Mark the following statements as true or false. a. The following is a valid \(\mathrm{C}++\) enumeration type: enum romanNumerals \(\\{I, V, X, L, C, D, M\\}\) b. Given the declaration: enum cars \(\\{\mathrm{FORD}, \mathrm{GM}, \text { TOYOTA, } \mathrm{HONDA}\\}\) cars domesticcars \(=\mathrm{FORD}\) the statement: domesticcars \(=\) domesticcars +1 sets the value of domesticcars to GM. c. \(A\) function can return a value of an enumeration type. d. You can input the value of an enumeration type directly from a standard input device. e. The only arithmetic operations allowed on the enumeration type are increment and decrement. The values in the domain of an enumeration type are called enumerators. g. The following are legal \(C++\) statements in the same block of a \(C++\) program: enum mathStudent \(\\{\mathrm{BILL}, \text { JOHN, LISA, RON, CINDY, SHELLY }\\}\) enum historyStudent \(\\{\mathrm{AMANDA}, \mathrm{BOB}, \mathrm{JACK}, \mathrm{TOM}, \mathrm{SUSAN}\\}\) h. The following statement creates an anonymous type: enum \(\\{\mathrm{A}, \mathrm{B}, \mathrm{C}, \mathrm{D}, \mathrm{F}\\}\) studentGrade i. You can use the namespace mechanism with header files with the extension h. j. Suppose str \(=" \mathrm{ABCD}^{\prime \prime} ;\) After the statement \(\operatorname{str}[1]=^{\prime} a^{\prime} ;\), the value of str is "aBCD". k. Suppose str = "abcd". After the statement: \(\operatorname{str}=\operatorname{str}+\) "ABCD" the value of str is "ABCD".

Short answer

a. True; b. True; c. True; d. False; e. False; f. True; g. True if distinct; h. True; i. False; j. False; k. False.

Step-by-step solution

Evaluate Part a

The statement `enum romanNumerals \(\{I, V, X, L, C, D, M\}\)` is a valid C++ enumeration type because it correctly follows the syntax for declaring an enumeration type, where `romanNumerals` is defined with enumerators `I, V, X, L, C, D, M`.

Evaluate Part b

The declaration `enum cars \(\{\mathrm{FORD}, \mathrm{GM}, \text { TOYOTA, } \mathrm{HONDA}\}\)` followed by `cars domesticcars = \mathrm{FORD};` initializes `domesticcars` to `FORD`. The operation `domesticcars = domesticcars + 1;` is syntactically valid and sets `domesticcars` to the next enumerator, which is `GM`, as C++ treats enumerators as integer values starting from 0.

Evaluate Part c

In C++, a function can return a value of an enumeration type just like any other data type. This makes the statement true.

Evaluate Part d

You cannot directly input an enumeration value from a standard input device using standard input functions like `cin`. Instead, you usually input a corresponding integer or string and then convert it to the enumeration type.

Evaluate Part e

The statement is false as you can perform other operations such as assignment, comparison, and explicit casting to integer on enumeration types. Only increment and decrement are specifically mentioned but aren't the only operations allowed.

Evaluate Part f

In C++, the values in the domain of an enumeration type are called enumerators. Therefore, this statement is true.

Evaluate Part g

Both `enum mathStudent \(\{\mathrm{BILL}, \text { JOHN, LISA, RON, CINDY, SHELLY }\}\)` and `enum historyStudent \(\{\mathrm{AMANDA}, \mathrm{BOB}, \mathrm{JACK}, \mathrm{TOM}, \mathrm{SUSAN}\}\)` are legal as long as they are within the same scope and have distinct enumerator names. This makes the statement true if all enumerator names are unique between the two enums.

Evaluate Part h

The statement `enum \(\{\mathrm{A}, \mathrm{B}, \mathrm{C}, \mathrm{D}, \mathrm{F}\}\) studentGrade` creates an anonymous enumeration type because it does not have a name for the enumeration itself, only for the variable `studentGrade`.

Evaluate Part i

You can use the namespace mechanism with headers by including them in a namespace block, but the statement appears to be asking about using file extensions which is unrelated to the usage of namespaces. This statement is false.

Evaluate Part j

After the statement `str[1] = 'a';`, the value of `str` is changed to `"aBCD"` because only the second character (`'B'`) is replaced with `'a'`.

Evaluate Part k

If `str = "abcd"`, and then the statement `str = str + "ABCD";` is executed, the new value of `str` becomes "abcdABCD" as it appends "ABCD" to the existing string.

Key concepts

Enumeration Types

In C++, an enumeration type, also known as an enum, is used to define a variable that can hold a set of predefined constants. Enumerations create a user-defined data type that consists of named integer constants. Typically, an enum is used when a variable can have one among a limited set of options, making it easy to read and maintain the code. For example, if you want to represent days of the week as integers, you can define an enumeration type like this:

enum Days { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };

In this example, each day is an enumerator within the enum `Days`. This means that `Sunday` becomes 0, `Monday` becomes 1, and so on until `Saturday`, which is 6. Enum types ensure that the variable only holds these specific values, providing both type safety and readability in your code. Enumerations are particularly useful when multiple variables should be able to take on these same constant values repeatedly across your application.

Enumerators

Enumerators in C++ are the constant values defined within an enumeration type. They act as identifiers for the integer values they represent. By default, the first enumerator is assigned the integer value 0, the second enumerator in the list gets the value 1, and so forth. However, you can manually assign values to enumerators if preferred.

If you have an enumeration like enum Status { Pending = 1, Approved, Rejected };, in this set, `Pending` will have the integer value 1, `Approved` will automatically get 2, and `Rejected` will be 3. Assigning explicit values like this can be helpful when aligning with specific requirements or existing systems.

The clarity that enumerators provide makes your code more understandable and less error-prone, ensuring it aligns exactly with the domain concepts you're modeling. Enumerators prevent magic numbers—unexplained and arbitrary constant values—from appearing throughout the code, enhancing maintainability.

C++ Syntax

The syntax in C++ for defining an enumeration involves using the `enum` keyword followed by an identifier for the enumeration type and a list of enumerators enclosed in braces. Here's a basic example:

enum Color { Red, Green, Blue };

In this syntax:

• The keyword `enum` suggests defining an enumeration.
• `Color` is the name of the enumeration type, ensuring we can declare variables of this type elsewhere in our code.
• The curly braces `{}` contain the enumerators `Red`, `Green`, and `Blue`.

C++ syntax allows you to declare variables of the enumeration type just as you would other types, e.g., Color myColor = Green; to set `myColor` to `Green`.

Enumerations are integral to maintaining clean and structured code in C++. Always remember to follow the C++ syntax carefully to avoid compilation errors and ensure the code executes as intended.

Function Return Types

In C++, functions can return various data types, including enumeration types. This flexibility allows a function to return a meaningful constant value that is part of an enum, instead of a simple integer or string. Making use of enumeration return types reinforces clarity and intent in your code.

Consider a function designed to check order status that may employ an enum like this:

enum OrderStatus { Pending, Processed, Shipped, Delivered }; OrderStatus CheckOrderStatus() { return Processed; }

In this situation, `CheckOrderStatus()` returns a value of type `OrderStatus`, specifically the `Processed` enumerator. This is beneficial because it clearly conveys what the function result represents without ambiguous numbers or strings.

Using enumeration types as function return types also strengthens the interface contract between different parts of a codebase. They specify what results a function can provide, reducing the likelihood of misinterpretation or incorrect usage by other developers.