Question

Find the error(s) in each of the following and explain how to correct it (them): a. Assume the following prototype is declared in class Time: void ~Time( int ); b. The following is a partial definition of class Time: class Time { public: // function prototypes private: int hour = 0; int minute = 0; int second = 0; }; // end class Time c. Assume the following prototype is declared in class Employee: int Employee( const char *, const char * );

Short answer

Part A: Remove 'void' and 'int'. Part B: Use a constructor for initialization. Part C: Remove 'int' from the constructor.

Step-by-step solution

Identify the Error in Part A

In part (a), the prototype is for a destructor. In C++, destructors do not have a return type and are declared with a tilde (~) followed by the class name. Thus, "void" before "~Time(int);" is incorrect. Destructors do not take parameters, so "int" should also be removed.

Correct the Error in Part A

To correct the error, remove the "void" type and the parameter from the prototype: "~Time();". This correctly declares a destructor without a return type and no parameters.

Identify the Error in Part B

In part (b), the issue is with the initialization of member variables directly in the class body (before the constructor definition), which was not allowed before C++11. For this declaration to be universally correct, initialization should occur in a constructor.

Correct the Error in Part B

To be compatible with all versions of C++, move the default initialization of member variables to the constructor of the class Time: ```cpp class Time { public: Time() : hour(0), minute(0), second(0) {} private: int hour; int minute; int second; }; // end class Time ``` This code declares a constructor to initialize the variables when a `Time` object is created.

Identify the Error in Part C

In part (c), the function prototype "int Employee(const char *, const char *);" is incorrect because constructors do not have a return type. This format suggests a constructor due to the same name as the class, but it incorrectly includes an "int" return type.

Correct the Error in Part C

To correct this error, remove the "int" return type from the constructor prototype: ```cpp Employee(const char *, const char *); ``` This properly declares a constructor for the Employee class which initializes using two string parameters.

Key concepts

Destructor Definition

In C++, a destructor is a special member function used to perform clean-up operations when an object of a class is destroyed. The key characteristics of destructors include:

• No return type. Destructors never return a value, unlike other functions. Including a return type is an error, as seen in the example "void ~Time(int);" where "void" should not precede the destructor.
• Declaration using a tilde (~) prefix followed by the class name. This specific syntax helps the compiler identify the function as a destructor.
• No parameters. Destructors are called automatically when an object goes out of scope or is deleted and should not accept any arguments.

When correcting a destructor prototype, it typically looks like this: `~ClassName();`. This ensures that your destructor adheres to the rules of not having return types or parameters, simplifying its automatic invocation processes.

Member Variable Initialization

Member variable initialization refers to setting initial values for variables defined within a class. Pre-C++11, variables in a class could not be initialized directly at the point of declaration, which would lead to errors if done so:

• Variables had to be assigned values within a constructor. This is because the constructor is called upon object creation, ensuring the variables are initialized.
• Post-C++11, in-class initialization has been allowed. However, for backward compatibility and ensuring broader code accessibility, relying on constructors for initialization can be favorable.

In the example "class Time", initializing with a constructor ensures compatibility: ``` class Time { public: Time() : hour(0), minute(0), second(0) {} private: int hour; int minute; int second; }; ``` This approach uses an initializer list with the constructor, which efficiently assigns initial values to member variables.

Constructor Prototypes

Constructors are fundamental to creating objects in C++. Like destructors, constructors have specific rules:

• No return type. This is crucial: constructors are not standard functions and should not return any value. Including a return type like "int" is incorrect and will cause errors, as observed in the "int Employee(const char *, const char *);" example.
• Same name as the class. A constructor needs to share its name with the class it belongs to, indicating its purpose to initialize new objects of the class.
• Can have parameters. Constructors can be overloaded, allowing for different initializations depending on how and with what data an object is created.

A corrected constructor prototype for class `Employee` should look like: `Employee(const char*, const char*);`. The absence of a return type and matching the function name with the class ensures it fulfills its role of initializing objects correctly.