C++

Question 1

What are the access modifiers in C++ ? Define each one of them

Answer 1

public : accessible from any part of the program (open bedroom)

private : can only be accessed from within the class or friend classes and functions (bedroom only for parents and their friends)

protected : just like private but can also be accessed by child classes (bedroom is open to parents, friends, and children)

Question 2

define encapsulation

Answer 2

bundling data and methods that work on that data into one unit (the class)

Question 3

what are the two types of polymorphism occuring under C++ ?

Answer 3

• compile-time polymorphism
• runtime polymorphism

Question 4

explain compile-time and runtime polymorphism

Answer 4

compile-time polymorphism is achieved by function or operator overloading

runtime polymorphism is achieved at runtime by overriding functions (virtual)

Question 5

define early binding and give a few other names for it
contrast it with late binding and explain the difference

Answer 5

In early binding, the compiler matches the function call with the correct function definition at compile time. It is also known as Static Binding or Compile-time Binding. By default, the compiler goes to the function definition which has been called during compile time.

In the case of late binding, the compiler matches the function call with the correct function definition at runtime. It is also known as Dynamic Binding or Runtime Binding. This can be achieved by declaring a virtual function.

Question 6

difference between class and struct ?

Answer 6

the only difference between a structure and a class is that structure members have public access by default and class members have private access by default

Question 7

what is a singleton ?

Answer 7

a class we plan to have only one instance of

Question 8

what is an interface ?

Answer 8

an interface in c++ is an abstract class. A class is made abstract by declaring at least one of its functions as PURE VIRTUAL (i.e virtual void doube f() = 0;)

Question 9

what is the purpose of an abstract class ?

Answer 9

The purpose of an abstract class (often referred to as an ABC) is to provide an appropriate base class from which other classes can inherit. Abstract classes cannot be used to instantiate objects and serves only as an interface. Attempting to instantiate an object of an abstract class causes a compilation error.

Thus, if a subclass of an ABC needs to be instantiated, it has to implement each of the virtual functions, which means that it supports the interface declared by the ABC. Failure to override a pure virtual function in a derived class, then attempting to instantiate objects of that class, is a compilation error.

Question 10

what is a simple difference between compile-time and runtime

Answer 10

errors can be detected without running the code at compile-time, and only through running at runtime

Question 11

How to cast away the constness of an int

Answer 11

const_cast(i) = 6;

Question 12

How to cast into constness

Answer 12

static_cast(j) = 7;

Question 13

what is #include called ?

Answer 13

a preprocessor directive == copy paste the iostream file at the beginning of our file

Question 14

what’s the purpose of the main function ?

Answer 14

tells the computer where to start

Question 15

output “hello world” to the console

Answer 15

cout &laquo_space;“hello world” &laquo_space;endl;

Question 16

what’s the purpose of the main’s return 0; ?

Answer 16

Says everything before it ran well

Question 17

how to print a new line insi;e the quotation marks ?

Answer 17

\n

Question 18

take in user input into variable a

Answer 18

cin&raquo_space; a;

Question 19

how do you define a function’s prototype and why

Answer 19

a function’s prototype lets the compiler know the function exists before it reads its definition.

Question 20

how can c++ tell a function is a constructor?

Answer 20

it has the same name as the class name (and no return type), gets called automatically when an instance is created

Question 21

why and how can we split our classes into separate files ?

Answer 21

easier to manage, potential for team work, modularity etc. We also compile the cpp into binary and only need to provide the prototype to users.

for each class create .h (prototypes) and .cpp (bodies), both files should have same #include

in main.cpp add #include

Question 22

what is :: ?

Answer 22

binary scope resolution operator&raquo_space; determines the namespace currently in use

Question 23

difference between ++x and x++ ?

Answer 23

if ++ before variable, runs the line of code then adds one to x, else adds then runs.

Question 24

for loop syntax

Answer 24

for(int x=1; condition; increment) { DO }

Question 25

calculate 5^2

Answer 25

include

cout &laquo_space;pow(5,2);

Question 26

difference between while loop and do while ?

Answer 26

do{THIS}while(CONDITION);

the semi-colon and running at least one time

Question 27

define a switch statement on the variable age

Answer 27

int age = 20;
switch(age){
case i:
do; break;
default:
do;
}

Question 28

logical and, or, not ?

Answer 28

&&
||
!

Question 29

what library contains rand() ?

Answer 29

include

Question 30

how to get [0,6] using rand()

Answer 30

rand%6+1

Question 31

How do we seed rand() ?

Answer 31

srand(seed);

better:
#include
srand(time(0));

Question 32

global variable v. local variable

Answer 32

one defined outside functions, one defined inside a function.

NB : functions prefer the nearest variable

Question 33

how do i use the global variable of same name from inside a function

Answer 33

using unary resolution operator ::tuna

Question 34

define function overloading

Answer 34

same name, different signature

Question 35

make a 5 int array using an initializer list

Answer 35

int bucky[5] = {2,3,4,5,6}

Question 36

how to define array as an argument to f

Answer 36

void f(int array[])

Question 37

how to define a multidimensional array

Answer 37

int x[2][3]= {{2,3,4},{3,5,6}}

Question 38

get the memory address of i

Answer 38

&i

Question 39

define pointer

Answer 39

a variable containing a memory address as its value

Question 40

point to i

Answer 40

int* ptr = &i;

Question 41

difference between passing by value, by reference and by pointer

Answer 41

by value, you pass a copy of the object

by reference, you pass the actual (constant, non null) memory address of the object

by pointer, you pass a pointer to the object you want (which can point elsewhere later, and be a nullptr)

Question 42

sizeof(x) returns ..

Answer 42

the size of x in bytes

Question 43

return len of array x

Answer 43

sizeof(x)/sizeof(x[0])

Question 44

what happens when a ptr is incremented

Answer 44

it points to the next element in memory (not to the next byte)

Question 45

what’s the purpose of :
#ifndef CLASS_H
#define CLASS_H

Answer 45

only include once

Question 46

when do you have to write A::A {}, A::somefunction{}, basically defining the scope you’re working in at every function definition

Answer 46

in the .cpp file, but not in the .h file (scope already obvious)

Question 47

call method() using ptr, a pointer to Class

Answer 47

ptr->method();

Question 48

implement a deconstructor

Answer 48

~Class();

no parameters, no return type, and no overloading

Question 49

CONST class instance requires ..

Answer 49

CONST methods

Question 50

How do we need to initialize constant attributes in a class constructor

Answer 50

member init syntax :

Class(int a, int b) : x(a), y(b) {}

Question 51

How to make a function your class’s friend

Answer 51

in class, class lets you sign as a friend

friend void f();

Question 52

what’s this ?

Answer 52

this is a pointer to the current class instance

Question 53

overload + to use it on myClass objects

Answer 53

MyClass operator+(MyClass c) :
MyClass a;
a.num=this->num+c.num
return(a);

Question 54

define accessibility in public, protected, and private inheritance :

Answer 54

public inheritance makes public members of the base class public in the derived class, and the protected members of the base class remain protected in the derived class.

protected inheritance makes the public and protected members of the base class protected in the derived class.

private inheritance makes the public and protected members of the base class private in the derived class.

NOTABENE: private members of the base class are inaccessible to the derived class.

Question 55

sizeof(char)

Answer 55

1 byte = 8 bits

Question 56

define a string s in C style

Answer 56

const char * s = “Hello”;

Question 57

a string in c++ is …

Answer 57

an array of chars

Question 58

difference between single and double quote strings

Answer 58

single: char, double: char ptr

Question 59

include string library

Answer 59

include

Question 60

how does the compiler know const char * c has ended in :

cout &laquo_space;c;

Answer 60

the nulle termination character \0

Question 61

declare a c++ string and find its size

Answer 61

std::string name = “Cherno”;
name.size();

Question 62

What does static mean outside a class ?
static int s_ = 5;

Answer 62

This variable is only going to be linked internally inside this translation unit

Question 63

How do you access a variable in another .cpp from main.cpp ? what if we mark it as static now ?

Answer 63

extern int s_;

If s_ is marked as static then the linker will not be able to resolve it. It is like it’s private to the translation unit it’s declared in.

Question 64

What does static mean inside a class ?

Answer 64

static var means there will only be one instance of the variable across all the instances of the class. Have to be defined outside the class.

static method can be called without a class instance, and it can’t use any non-static class members since if no instance, that would make no sense

Question 65

What are enums and how are they used ?

Answer 65

They are user-defined types that can take only one of few values (integer-like), increment from 0 by default unless defaulted

enum Example : unsigned char {A=0,B,C};

Example value = B;
if (value==1) { // DO }

Question 66

A const variable must be initialized …

Answer 66

At definition

Question 67

State two possible uses for the keyword “mutable”

Answer 67

1. declaring a class variable as mutable allows const functions to modify it
2. auto f = = mutable {x++;}

Question 68

A string’s end is marked using … ?

Answer 68

a null termination character ‘\0’

Question 69

What’s the use of member initialization list ?

Answer 69

Resource acquisition is initialization

We construct and give value at same time instead of calling constructor twice

Question 70

How do you instantiate an object of class Entity ? Give different possibilities

Answer 70

1. Entity entity = Entity(“cherno”);
   // stack, scoped, small (1MB)
2. Entity* e = new Entity();
   // heap, slower, must free later

is my object big ? do i want to explicitly control the lifetime of my object ?

Question 71

memcpy params ?

Answer 71

memcpy(dest, src, size)