Question

Given: enum currencyType \\{DOLLAR, POUND, FRANK, LIRA, MARK); currencyType currency; which of the following statements are valid? a. currency = DOLIAR b. \(\quad\) cin \(>>\) currency c. currency \(=\operatorname{static}_{-}\) cast \(\langle\text {currencyType }>(\text { currency }+1)\) d. for (currency = DOLLAR; currency \(<=\) MARK; currencyt+) cout \(<<\) "*";

Short answer

Statements c is valid; statements a, b, d are invalid.

Step-by-step solution

Analyze Statement a

Statement a is `currency = DOLIAR`. In this statement, `DOLIAR` is a typo. The correct enum value should be `DOLLAR`. Since `DOLIAR` is not a defined enumerator, this statement is invalid.

Analyze Statement b

Statement b is `cin >> currency`. In C++, `cin` can be used to input data into a variable, but directly inputting into an enum type like this requires operator overloading which is not inherently available. Therefore, this statement is invalid unless appropriately overloaded.

Analyze Statement c

Statement c is `currency = static_cast(currency + 1)`. This statement performs a type conversion using `static_cast`. It is valid if `currency + 1` results in a value that falls within the range of the defined enumerators (e.g., going from `DOLLAR` to `POUND`). Therefore, this statement is valid, assuming you don't go out of bounds.

Analyze Statement d

Statement d is `for (currency = DOLLAR; currency <= MARK; currency++) cout << "*";`. The syntax `currency++` assumes incrementing an enum value, and back to a valid enum. In most cases, this might be valid in C++ with correct incremental logic; however, there's a typo `currencyt+`, making this statement invalid as presented due to the typo.

Key concepts

enum data type

In C++, enumerations, commonly known as enums, provide a way to define variables that can only take certain discrete values, improving code readability and reducing errors. They belong to the user-defined data types category. Declaring an enum involves naming the enumeration and listing the possible values, enclosed in curly braces. For example, `enum currencyType {DOLLAR, POUND, FRANK, LIRA, MARK};` defines a new enum type, `currencyType`, with possible values like DOLLAR, POUND, and so on.

Enums help in scenarios where a variable can take only one out of a small set of possible values. As each enum value is represented as an integer, they are efficient and offer a type-safe way to handle states or modes in programs, without the overhead of strings or other more complex data types. By default, the first enumerator has the integer value 0, the second one 1, and so forth, unless explicitly assigned another value.

input with cin

The `cin` object in C++ is used for input from the standard input, typically the terminal. It streams data into variables. However, when dealing with enum types, directly binding a value to an enum variable using `cin` can be tricky, as C++ doesn't inherently know how to read characters and convert them into an enum value.

To input data into an enum, you usually need a workaround, such as using integer values with `cin` that correspond to the enum values' underlying integers, or string inputs followed by a conversion into enum types with conditional checks or operator overloading. This means the statement `cin >> currency;` won't work as expected for an enum type without additional code to map input to the enum.

static_cast in C++

The `static_cast` operator in C++ is used to perform safe cast conversions between compatible types. It's particularly helpful when you need to convert between integer values and enum types. Using `static_cast(currency + 1);`, you attempt to convert the numeric result of `currency + 1` back to an enum type.

This method is instrumental when cycling through enum values sequentially, ensuring that the arithmetic operation on the enums is safely interpreted back as an enum. Still, you must handle the boundaries properly to avoid converting to an undefined enum value. Always check that the result of such an operation remains within the defined range of the enumeration before assigning it back.

incrementing enumerators

Enumerators in C++ behave like integers, which means they can be incremented using typical arithmetic operators. This is often done in loops to iterate through the values of an enumeration, as attempted in the code snippet `for (currency = DOLLAR; currency <= MARK; currency++)`. This pattern is valid if you ensure each incremented value still corresponds to a defined enumerator within the enum.

However, incrementing blindly without bounds checking might lead to runtime issues if the incremented value surpasses the last defined enumerator. Careful control structures and boundary checking ensure that such operations stay valid and meaningful within context. By utilizing enums in loops, developers gain a clear, efficient method of handling state changes and mode checks in their code.