C++ Classes

Question 1

Though functionally identical, what is the biggest difference between structs and classes?

Answer 1

Class defaults to private, while struct defaults to public

Question 2

What is the difference in use case between structs and classes

Answer 2

Classes are best for data abstraction and inheritance, while structs are best used for data grouping and access.

Question 3

What are the two basic constructors?

Answer 3

Default (no args) and with input

Question 4

What is the abbreviation of Constructor?

Answer 4

CTOR

Question 5

What are the non-basic Constructors?

Answer 5

• Copy
• Assignment
• Move
• Move Assignment

Question 6

What is Uniform Initialization Syntax

Answer 6

The standard ways of constructing objects and variables in c++

Question 7

What are the Uniform initialization Syntax ctors?

Answer 7

Default, Empty, Initializer List, Assignment

Question 8

What is the following Ctor? string x;

Answer 8

default

Question 9

What is the following Ctor? string x{};

Answer 9

Empty

Question 10

What is the following Ctor? string x{“string”};

Answer 10

Initializer List

Question 11

What is the following Ctor? string x = “string”;

Answer 11

Assignment

Question 12

How do you define a Class?

Answer 12

class MyClass{
//private fields
int num1;

public:
MyClass() {num1 = 1;}
int get_num1() { return this->num1;}
};

Question 13

How do you define a Struct?

Answer 13

struct MyStruct{
//public fields
MyStruct() {num1 = 1;}
int get_num1() { return this->num1;}

private:
int num1;
};

Question 14

What is the “this” keyword?

Answer 14

It is a pointer to the current object

Question 15

What is the syntax for using the “this” keyword?

Answer 15

this->

Question 16

Given class MyClass, how do you set the output of the class (like toString in Java)

Answer 16

ostream& operator«(ostream &out, const MyClass &m) {
//return desired output. Ex:
return out &laquo_space;m.get_x() &laquo_space;“,” &laquo_space;m.get_y();
}

Question 17

What is the constructor keyword “=default”?

Answer 17

Keeps the default version of a ctor.

Question 18

What is the ctor keyword “=delete”?

Answer 18

Deletes ctor and prevents it from ever being defined. (also provideds a ‘deleted’ message)

Question 19

What is Member Initialization?

Answer 19

Pre-allocating values in the contructor.

Question 20

What is the order of member initialization?

Answer 20

In the order that the variables were declared in the class.

Question 21

When does Member pre Initialization occur?

Answer 21

Before the curly braces in a constructor statement.
Ex: Circle() : /*member initialization*/ {}

Question 22

What MUST be member initialized?

Answer 22

• Const values
• objects with no default ctor
• Reference Variables
• Any call to parent / base class

Question 23

Why must const values be member initialized?

Answer 23

The compiler will set them to a default if not, and then they cannot be changed.

Question 24

Why must objects without a default ctor be member initialized?

Answer 24

Because otherwise there is no default value they can be assigned.

Question 25

Why must reference variables be member initialized?

Answer 25

Because there is no logical default for a memory reference.

Question 26

What is Constructor Delegation?

Answer 26

It is essentially constructor chaining. Ex:
Circle::Circle() : Circle(1) { }
Circle(int radius) : Circle (1, 1, radius) { }
Circle(int x, int y) : Circle (x, y, 1) { }
Circle(int x, int y, int radius) : Circle (x, y, radius) { }

Question 27

What is a Default Value in classes / structs?

Answer 27

When the variables are assigned values as they are declared outside of ctor.

Question 28

What are Default Constructor Arguments?

Answer 28

When variables are directly assigned in the ctor. Ex:
Circle(int x=1, int y=1, int radius=1) : x(x), y(y), radius(radius) { }

Question 29

What is the limiting factor of Default Constructor Arguments?

Answer 29

If variable values are provided in the ctor call, it must be in order. Removes some possible call options.

Question 30

What is a const Variable?

Answer 30

A variable that, once allocated, can never be changed.

Question 31

What is a const Method?

Answer 31

Methods that cannot change the data members of the class.

Question 32

What is the most common example of const methods?

Answer 32

Getters.

Question 33

How do you declare given method ‘MyMethod’ to be const?

Answer 33

int MyMethod() const {…}

Question 34

How do const arguments work?

Answer 34

Create an agreement that data stored in the const variable will not be changed. Important when using ‘pass by reference’.