Question

Give the definition for the constructor discussed at the end of the previous section. The constructor is to be added to the class Money in Display 11.5 The definition begins as follows: Money::Money(double amount) {

Short answer

Answer: The constructor in the class Money converts the double input amount into dollars and cents by first multiplying the input amount by 100 and rounding it to the nearest whole number to get the total cents. Then, it calculates the number of dollars by dividing the total cents by 100 and obtains the remaining cents using the modulus operator.

Step-by-step solution

Initialize Constructor

In the class Money, we'll start by initializing the constructor with the given code: ``` Money::Money(double amount) { } ```

Convert the Amount to Cents

Next, we will convert the given amount of money into cents. Here, we will multiply the input amount by 100, rounding it to the nearest whole number, as cents are represented as integers. ``` Money::Money(double amount) { // Convert dollars to cents and round to the nearest whole number int totalCents = static_cast(round(amount * 100)); } ```

Calculate Dollars and Cents

Now we can obtain the dollars and cents separate from the total cents. To find the number of dollars, we will divide the total cents by 100. To find the remaining cents, we will use the modulus operator. ``` Money::Money(double amount) { // Convert dollars to cents and round to the nearest whole number int totalCents = static_cast(round(amount * 100)); // Find the number of dollars and the remaining cents dollars = totalCents / 100; cents = totalCents % 100; } ``` Now, the constructor is defined and should correctly initialize the class Money with the given double amount.

Key concepts

class implementation

When designing programs in C++, one of the fundamental concepts you'll work with is class implementation. A class in C++ acts as a blueprint for creating objects. It encapsulates data for the object and methods to manipulate that data. Let’s consider how the class is set up and how we can implement it effectively.

The syntax to declare a class starts with the keyword `class`, followed by the class name and a pair of curly braces `{}` enclosing the class's body. For our exercise, we are discussing the `Money` class. This class is likely to contain member variables, such as `dollars` and `cents`, and member functions, which include constructors and other methods that operate on the class's data.

The main goals when implementing a class are to ensure encapsulation, clarity, and usability. This involves protecting the internal state of the object by accessing it only through public member functions, ensuring that only the correct operations can be performed on the data. This setup allows for better maintenance and use of the class within a program.

data types

Data types play a crucial role in how variables in a C++ program are defined, stored, and operated upon. They are essentially labels that define the type of data a variable can hold, such as integers, floating-point numbers, and more.

For the `Money` class, understanding the appropriate data types is essential. In the context of this exercise, the constructor initially takes an argument of type `double` to represent the amount. A `double` is a floating-point data type that can represent decimal numbers with precision. This allows us to handle values such as $10.99 precisely.

However, since cents are best represented as whole numbers, we have to perform a type conversion during the construction to handle the decimal to integer conversion efficiently. The `static_cast` operation is used to convert the double value of dollars to an integer representing cents, ensuring we handle any precision errors by rounding before casting. These decisions on data types help manage the varying needs of different parts of a program, ensuring both precision and accuracy where needed.

object initialization

Object initialization is the process of setting up an object with an initial state when it is created. In C++, constructors are special member functions that are invoked automatically when an object is created. Their main purpose is to initialize the newly created object.

The constructor for the `Money` class is explicitly called `Money::Money(double amount)`. It uses the passed `amount`, a double representing dollars and possibly cents, and initializes the class variables `dollars` and `cents` accordingly. This initialization process involves converting the `amount` to `cents` by multiplying by 100 and then rounding the result to ensure no fractional cents exist.

The constructor then calculates how many whole dollars and remainder cents are present in the integer `totalCents`. By dividing by 100, we get the dollars, and using the modulus operator, we derive the remainder for `cents`. Initializing objects properly ensures they can be used reliably and as intended in further operations within your program.