Default constructor in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a default constructor in C++?

A default constructor is a special constructor that can be called with no arguments. It initializes objects with default values.

beginner

How does the compiler behave if you don't define any constructor in a class?

The compiler automatically provides a default constructor that initializes members with default values if no constructor is defined.

beginner

Write a simple class with a default constructor that prints a message when called.

#include <iostream>
class MyClass {
public:
    MyClass() { std::cout << "Default constructor called\n"; }
};

intermediate

Can a default constructor have parameters?

Yes, but all parameters must have default values so that the constructor can be called without arguments.

intermediate

What happens if you declare a constructor with parameters but no default constructor?

The compiler does not generate a default constructor automatically, so you cannot create objects without arguments unless you define one explicitly.

What is the main purpose of a default constructor?

A To initialize an object without any arguments

B To copy an object

C To destroy an object

D To overload operators

A default constructor initializes an object when no arguments are provided.

If you define a constructor with parameters but no default constructor, what happens when you try to create an object without arguments?

A It works fine

B The compiler creates a default constructor automatically

C Object is initialized with garbage values

D Compiler error: no matching constructor

Without a default constructor, creating an object without arguments causes a compiler error.

Which of these is a valid default constructor declaration?

A MyClass(int x = 0);

B MyClass();

C Both B and C

D MyClass(int x);

A constructor with no parameters or with all parameters having default values can act as a default constructor.

What does the compiler do if no constructor is defined in a class?

A It refuses to compile

B It creates a default constructor automatically

C It creates a destructor automatically

D It creates a copy constructor automatically

The compiler provides a default constructor if none is defined.

Which of the following statements about default constructors is FALSE?

A Default constructors always initialize members to zero

B Default constructors can have parameters with default values

C Default constructors can be user-defined

D If no constructor is defined, the compiler provides a default constructor

Default constructors do not always initialize members to zero; uninitialized members may have garbage values unless explicitly initialized.

Explain what a default constructor is and when the compiler provides one automatically.

Think about how objects are created without giving any values.

Describe what happens if you define a constructor with parameters but do not define a default constructor.

Consider what happens when you try to create an object with no arguments.