C++

Question 1

True or False?
A constructor has to return a value

Answer 1

False
A constructor has no return type
(not even void)

Question 2

True or False?
A constructor must have the same name as the class

Answer 2

True

Question 3

True or False?
A constructor can not take arguments

Answer 3

False

Question 4

True or False?
A constructor can be overloaded

Answer 4

True
A class can have multiple constructors

Question 5

Explain “constructor”
in 3 short statements

Answer 5

Constructor:
- Same name as the class
- No return type
- Initializes the member variables

Question 6

True or False?
Abstract classes can only have pure virtual methods

Answer 6

False
Abstract classes must have at least one pure virtual method.
But it can have a mix of pure virtual, virtual and non-virtual methods

Question 7

True or False?
You can not create objects from an abstract class

Answer 7

True
An abstract class can not be initilialized directly

Question 8

What makes a class abstract?

Answer 8

It has at least one pure virtual method

Question 9

Explain encapsulation

Answer 9

Encapsulation promotes modularity by allowing the internal details of a scope to be modified without affecting other parts of the program
Ex. Changes to the internal variables are isolated within the scope, and won’t be changed outside and variable created within a scope only exists within that scope.

Question 10

True or false?
A class’ static methods can access private member variables of the class

Answer 10

False
Static methods of a class do not have access to the private member variables of the class directly

Question 11

Explain private member

Answer 11

Private members are only accessible within the scope of the class itself

Question 12

Explain protected member

Answer 12

A protected member is accessible within the class that declares it and by classes derived from it
However, it is not accessible from outside the class hierarchy

Question 13

Explain public member

Answer 13

The public access specifier allows members of the class to be accessed from outside the class definition

Question 14

Explain Pure virtual Methods

Answer 14

A pure virtual method is a virtual function that has no implementation in the base class and is meant to be overridden by derived classes

It is declared with the = 0 syntax at the end of its declaration.

Ex.
virtual void pureVirtualMethod() = 0;

Question 15

Explain virtual Methods

Answer 15

A virtual method is a member function of a class that can be overridden in a derived class

When a method is declared as virtual in a base class, it allows a derived class to provide its own implementation of that method

Ex.
virtual void virtualMethod()
{
std::cout«“Hello”«std::endl;
}

Question 16

Explain static methods

Answer 16

Static method:
- A member function of a class that is associated with the class itself rather than an instance of the class
- A static method can be called on the class itself, rather than on an object of the class
- Static methods are declared using the static keyword

Ex.
static void staticMethod()
{
std::cout «“This is a static method.”«std::endl;
}

Question 17

Explain overriding

Answer 17

Overriding:
- Allows a derived class to provide a specific implementation for a method that is already defined in its base class
- The overridden method in the derived class must have the same signature (name, return type, and parameters) as the method in the base class

Ex.
void virtualMethod() const override
{
std::cout«“DerivedClass::virtualMethod()”«std::endl;
}

Question 18

Explain function overloading

Answer 18

Function overloading allows you to define multiple functions with the same name but different parameter lists.

(The compiler determines which function to call based on the number, types, and order of the arguments passed during the function call.)

Question 19

what concept does the following code demonstrate?

class A
{
void print (int i)
{
std :: cout &laquo_space;“print: “ &laquo_space;i endl;
}
};

class B : class A
{
void print (float f)
{
std :: cout &laquo_space;“print again: “ &laquo_space;f endl;
}
};

a) Overriding
b) Encapsulation
c) Overloading
d) Polymorphism

Answer 19

c) Overloading

You can still call print on an object of class B with an int as parameter, in that case the method in the base class will be called.

Ex.
B objB;
objB.print(42); // Calls A::print(int)
objB.print(3.14f); // Calls B::print(float)

Question 20

Explain polymorphism
- Compile-time (Static) Polymorphism
- Runtime (Dynamic) Polymorphism

Answer 20

Polymorphism allows objects of different types to be treated as objects of a common base type

Compile-time (Static) Polymorphism:
- Also known as function overloading and operator overloading
- Occurs at compile time
- Multiple functions or operators with the same name but different parameter types or a different number of parameters
- The compiler determines which function or operator to call based on the arguments provided

Runtime (Dynamic) Polymorphism:
- Achieved through virtual functions and inheritance
- Occurs at runtime
- Allows a base class pointer or reference to refer to objects of derived classes

Question 21

Explain composition

Answer 21

Composition represents a “has-a” relationship, indicating that an object is composed of other objects

Ex. A car has an engine and 4 wheels

Question 22

Syntax for calling the superclass A method x() from subclass B

Answer 22

A::x();

Question 23

Explain Struct

Answer 23

A struct is like a class, but the default access control is set to public

Question 24

Fields and methods of a struct is by default:
a) Private
b) Public
c) Protected
d) Secured

Answer 24

b) Public

Question 25

Fields and methods of a class is by default:
a) Private
b) Public
c) Protected
d) Secured

Answer 25

a) Private

Question 26

int x = 5;
Create a reference variable to x.

Answer 26

int &ref = x;

Question 27

What is the memory area called where dynamic allocations are stored?

Answer 27

Heap

Question 28

What is the memory area called where static allocations are stored?

Answer 28

Stack

Question 29

Syntax to dynamically allocate an objact of class A?
Syntax to deallocate that memory?

Answer 29

A *a = new A;
delete a;

Question 30

Syntax to dynamically allocate an array of objects of class A?
Syntax to deallocate that memory?

Answer 30

A *arrayA = new A[5];
delete[] arrayA;

Question 31

True or False?
In case of inheritence, when an object of an derived class is created then the base class constructor will be imvoked first followed by the derived class constructor.

Answer 31

True

Question 32

True or False?
You can only insert elements at the beginning of linked lists.

Answer 32

False

In a linked list, you can insert elements at various positions, not just at the beginning. The ability to insert elements at different positions is one of the advantages of using linked lists.

Question 33

Explain default constructor

Answer 33

A default constructor is a constructor that is automatically generated by the compiler if no constructor is provided in a class

Question 34

Explain Member Initializer List

Answer 34

The member initializer list is used in the constructor to initialize class members before the constructor body executes.

Ex.
class MyClass {
private:
int x;
public:
MyClass(int value) : x(value) {
// Member initializer list
}
};

Question 35

Explain function pointer

Answer 35

A function pointer is a variable that stores the address of a function.

ex.
void Foo() {
//implementation
}
void (*funcPtr)() = &Foo;

General:
functionReturnType (*pointerName)(functionParameters) = &functionName

Question 36

Explain pointer

Answer 36

A pointer is a variable that holds the memory address of another variable.

ex
int x = 5;
int *xptr = &x;

Question 37

Explain Linked List

Answer 37

A linked list is a data structure consisting of nodes where each node contains data and a reference (link) to the next node in the sequence.

(It provides dynamic memory allocation and efficient insertions/deletions.)

Question 38

Explain Reference Variable

Answer 38

A reference variable is an alias for an existing variable.

It provides an alternative name for a variable and is often used in function parameters to pass values by reference.

ex.
int x = 5;
int &ref = x;

Question 39

Why is polymorphism needed in object oriented programming?

Answer 39

Polymorphism in object-oriented programming allows for code flexibility by enabling objects of different classes to be treated as objects of a common base class.
It supports more adaptable code, making it easier to manage and extend systems.

Question 40

What does dynamic binding have to do with polymophism?

Answer 40

Dynamic binding in polymorphism refers to the ability of the program to determine at runtime which method or function to invoke based on the actual type of the object.

when a base class declreas a method as virtual and a sub class overrides it, the actual method to be called is determined at runtime based on the type of object being referred to (polymorphism)

Question 41

What are pass-by-value and pass-by-reference?

Answer 41

Pass-by-value involves passing the actual value of a variable to a function. Pass-by-reference involves passing the memory address (reference) of a variable to a function,
allowing the function to directly modify the original variable.

ex pass-by-value:
int Foo (int value){
//implementation
}
int x = 3;
Foo(x);

ex pass-by-reference:
int Foo (int &value){
//implementation
}
int x = 3;
Foo(x);

Question 42

How are pass-by-value and pass-by-reference used?

Answer 42

In pass-by-value, a copy of the variable is passed to a function. Changes within the function don’t affect the original variable.
In pass-by-reference, the memory address of the variable is passed, allowing the function to modify the original variable directly.

Question 43

What are dynamic allocations in C++?

Answer 43

Dynamic allocations in C++ involve allocating memory at runtime using operators like new and delete. It allows flexible memory management and is commonly used for creating objects on the heap.

Question 44

How do you dynamically allocate and deallocate memory?

Answer 44

Dynamically allocate memory in C++ using new and deallocate it using delete.

Example
int *array = new int[5];
delete[] array;

Question 45

What is a memory leak?

Answer 45

A memory leak occurs in programming when a program allocates memory but fails to deallocate or release it, leading to a gradual increase in the program’s memory usage and potential performance issues.

Typically this happens when memory is dynamically alloceted and not deallocated.

Question 46

Can you leak memory without dynamic allocations?
If so, an give example

Answer 46

Yes, for example when a program opens a file and forgets to close it.

Question 47

What is the purpose of encapsulation in object oriented programming?

Answer 47

The purpose of encapsulation in object-oriented programming is to bundle data and methods that operate on the data into a single unit, known as a class.
Encapsulation promotes information hiding, code organization, and maintenance.

Question 48

Give a code-example of encapsulation
(Do this on paper, there will be an example given to compare with when you klick on this card)

Answer 48

class Person {
private:
std::string name;
int age;

public:
// Public methods to access and modify private members
void setName(string newName) {
name = newName;
}

std::string getName() const {
    return name;
}

void setAge(int newAge) {
    if (newAge >= 0) {
        age = newAge;
    } else {
        std::cout << "Invalid age!" << std::endl;
    }
}

int getAge() const {
    return age;
} };

Question 49

True or False?
Non-static methods can use static fields

Answer 49

True

Explanation:

Non-static methods can access static fields in a class. Static fields are associated with the class itself rather than with instances of the class. Therefore, both static and non-static methods can access static fields.

Question 50

Which of the following can be used to call a superclass A method x() from a subclass B?
a) A.x()
b) A->x()
c) A::x()
d) this->x()

Answer 50

c) A::x()

Question 51

Choose the correct pure virtual method definition from the following.
a) virtual void f() : 0;
b) void virtual f()=0 { }
c) virtual void f() {} = 0;
d) None of the above

Answer 51

d) None of the above

It should be:
virtual void f() = 0;

Question 52

What is/are true about abstract classes?
a) They can only have pure virtual methods
b) You cannot create objects from them
c) They can be used in polymorphism
d) A & B
e) B & C
f) A, B & C

Answer 52

e) B & C

You cannot create objects from them
They can be used in polymorphism

Question 53

Which of the following statements is/are true about constructor:
a) It must have same name than the class
b) It has no return value
c) There can be only one constructor in a class
d) A and B
e) A, B and C

Answer 53

d) A and B

It must have same name than the class
It has no return value

Question 54

Which of these pairs represents composition?
a) Car – Engine
b) Car – Motorcycle
c) Car – Vehicle
d) Car – Road

Answer 54

a) Car – Engine

Question 55

Fields and methods of a class are by default:
a) private
b) public
c) protected
d) secured

Answer 55

a) private

Question 56

Which of the following shows a correct way to declare a reference variable?
a) int &x = 5;
int ref = x;

b) int x = 5;
int ref = &x;

c) int x = 5;
int &ref = x;

d) int *x = 5;
int &ref = &x;

Answer 56

c) int x = 5;
int &ref = x;

Question 57

Which of the following is the correct way to dynamically allocate memory for an int variable?
a) int *i = new int();
b) int i;
c) int &i = new int;
d) int *i = new int;

Answer 57

a) int *i = new int();
eller
d) int *i = new int;

Question 58

What is the memory area called where function calls are stored?
a) Dump
b) Heap
c) Stack
d) Pile
e) Queue

Answer 58

c) Stack

Question 59

In case of inheritance, when an object of a derived class is created then___________ .
a) only the derived class’ constructor will be invoked
b) only the base class’ constructor will be invoked
c) the derived class’ constructor will be invoked first followed by the base class’ constructor
d) the base class’ constructor will be invoked first followed by the derived class’ constructor

Answer 59

d) the base class’ constructor will be invoked first followed by the derived class’ constructor

Question 60

If the base class has a constructor with arguments, then it is ________________ for the derived class to
have a constructor and pass the arguments to the base class constructor.
a) Mandatory
b) Optional
c) Compiler dependent
d) Error

Answer 60

a) Mandatory

Example:
class Base {
public:
Base(int v){}
};

class Derived : public Base {
public:
Derived(int derivedV, int baseV) : Base(baseV){}
};

Question 61

Which form of delete is used to deallocate a dynamically allocated array?
a) delete array
b) delete *array
c) delete array[]
d) delete[] array

Answer 61

d) delete[] array

Question 62

class Derived : public Base {
// Other code here
};

what does it mean when using public above?

Answer 62

Public Members of class Base are still accessible as public in Derived class

Question 63

class Derived : protected Base {
// Other code here
};

what does it mean when using protected above?

Answer 63

Public Members of class Base are now accessible as protected in Derived class

Question 64

class Derived : private Base {
// Other code here
};

what does it mean when using private above?

Answer 64

Public and protected Members of class Base are now private in Derived class

Question 65

Explain Default constructor

Answer 65

When no constructor is created within a class it’s given a default constructor which looks like this:

class Foo {
Foo(){}
};

no parameter and no initialization

Question 66

Explain Initializer list

Answer 66

Initialziser listcan refer to a member initializer list (the one for a constructor) or any other initializer list (like the one for an array or vector).
It is essentially a list where the values are initialized.

example iwth member initializer list:
It is a part of the constructor, and a way to initialize values of member variables when a new instance of the class is created.

class MyClass {
private:
int x;
int y;

public:
// Constructor with initializer list
MyClass(int a, int b) : x(a), y(b)
//this will set vaules to x and y as the instance is created
{
// Other constructor code
}
};

Question 67

What are function pointers in C++?

Answer 67

Function pointers in C++ are variables that store addresses of functions. They enable dynamic selection and invocation of functions at runtime. Function pointers can be useful for implementing callbacks, creating function tables, and achieving greater flexibility in program design.

Question 68

How can memory leaks be prevented (give a code example)?

Answer 68

By always deleting dynamically allocated memory, suggestingly in a deconstructor so it won’t be forgotten.
And by always closing an opened file.

Example:

class Person {
private:
std::string* name;
int* age;

public:
Person(std::string newName, int newAge) :
name(new std::string(newName)),
age(new int(newAge)) {}
~Person() {
delete name;
delete age;
}
};

Question 69

Explain pointer

Answer 69

A pointer in programming is a variable that holds the memory address of another variable
Ex.
int x = 10;
int *ptr = &x;

Question 70

Explain reference variable

Answer 70

A reference variable in programming is an alias or alternative name for an existing variable.
It allows you to refer to the same memory location as another variable, providing a convenient way to access or modify the data without duplicating it.

Ex.
int x = 10;
int &ref = x;