Question

Suppose your program contains the following class definition (along with definitions of the member functions): class Yourclass \\{ public: YourClass(int new_info, char more_new_info); Yourclass(); void do_stuff( \()\) private: int information; char more_information; \\} Which of the following are legal? YourClass an_object(42, 'A'); YourClass another_object; YourClass yet_another_object() \\[ \begin{array}{l} a n_{-} \text {object }=\text { Yourclass }\left(99, \quad^{\prime} B^{\prime}\right) ; \\ a n_{-} \text {object }=\text { Yourclass }() ; \\ \text { an_object }=\text { YourClass } \end{array} \\]

Short answer

Answer: The legal statements are: 1. YourClass an_object(42, 'A'); 2. YourClass another_object;

Step-by-step solution

Understand the Class Definition

The class definition has two constructors: one with two parameters(int and char) and the other one is default. The class also has a function called do_stuff() which takes no arguments. Private data members are 'int information' and 'char more_information'. Step 2: Evaluate each provided statement

Examine Each Statement

We have three statements to evaluate: 1. YourClass an_object(42, 'A'); 2. YourClass another_object; 3. YourClass yet_another_object(); Step 3: Verify the legality of each statement

Analyze the Legality of Each Statement

1. YourClass an_object(42, 'A'); - This statement is legal because it uses the provided constructor YourClass(int new_info, char more_new_info), with 42 as an int and 'A' as a char. 2. YourClass another_object; - This statement is legal, as the default constructor Yourclass() is available in the class definition. 3. YourClass yet_another_object(); - This statement is not legal. It appears as if it is trying to use the default constructor, but the syntax is incorrect. The parentheses at the end make the statement look like a function declaration, which is not what we want. The correct statement would be: YourClass yet_another_object; Step 4: Check the other given expressions

Examine Other Expressions

1. an_object = YourClass(99, 'B'); - This statement is not legal, because the object 'an_object' has already been constructed, and we cannot assign a new object of the same class to an existing object in this manner. 2. an_object = YourClass(); - This statement is also not legal for the same reason as the previous one. We cannot reassign a new object to an already existing object. 3. an_object = YourClass; - This statement is not legal, because it is trying to assign the class itself to the object which is not possible. We can only assign objects or their references, but not the class itself. Step 5: Summarize the findings

Summarize Legal Statements

Based on the analysis, the following statements are legal: 1. YourClass an_object(42, 'A'); 2. YourClass another_object;

Key concepts

Object Instantiation

Object instantiation in C++ is the process of creating an actual object from a class blueprint. Think of a class as the blueprint for a house, and instantiating an object as the actual building of the house. In the context of the provided exercise, object instantiation occurs when we declare YourClass an_object(42, 'A'); and YourClass another_object;. The first creates an object with specific information, using parameters passed to the constructor, like giving custom specifications for your new house. The second statement uses the default constructor, similar to building a house with default settings.

The instantiation process is crucial in C++ as it brings to life the defined class by allocating space in memory for the object and setting up the initial state of the object using constructors.

Default Constructor

A default constructor in C++ is a constructor that can be called with no arguments. It is automatically called when an object is created without any specified parameters, like YourClass another_object; in our exercise. If you don't provide a constructor for your class, C++ generates a default constructor automatically. This constructor initializes class members with default values like zeros for numbers, null for pointers, and so on. In the provided class, the default constructor is explicitly declared using YourClass();.

Default constructors are particularly useful for creating objects when you don't have initial values for all the member variables or simply want an object with the default state.

Constructor Overloading

Constructor overloading in C++ is the concept of having more than one constructor with different parameters. It allows the creation of objects in different states. Think of it as different ways to build your house; you could choose a pre-designed model or customize it to your liking. The class in the exercise has two constructors: YourClass(int new_info, char more_new_info); and YourClass();, meaning it can be instantiated with either specific details or with default settings. Constructor overloading is an example of polymorphism, a core concept in C++ that increases flexibility in your code.

Class Members Visibility

In C++, class members can have different visibility levels, commonly known as 'access specifiers'. The provided exercise uses two: public and private. Public members, like YourClass(int new_info, char more_new_info); and YourClass();, are accessible from anywhere outside the class where the object is visible. This is akin to a public announcement that everyone can hear.

On the other hand, private members like int information; and char more_information; can only be accessed by member functions of the same class or friends of the class. It's like having private conversations within your household. Understanding the access levels is crucial for protecting the data integrity of your objects and encapsulating the implementation details.

C++ Syntax Errors

Syntax errors in C++ occur when the code deviates from the correct structure or rules defined by the language. They are like grammatical errors in a spoken language. The exercise shows a common mistake with YourClass yet_another_object(); which looks deceptively correct but is actually a syntax error due to the unnecessary parentheses. This would cause a compiler error, as it's attempting to declare a function rather than instantiating an object. To avoid syntax errors, it's important to carefully follow the rules of C++ syntax, such as correctly placing semicolons, using the right type of brackets, and matching class constructors as defined. Check and double-check your code often to catch these errors early in the development process.