337 C++ (20-21)

Question 1

What do you need to include in order to use cin and cout?

Answer 1

#include <iostream>

Question 2

What is the correct way to write cin and cout. (What is the extraction and insertion operator?)

Answer 2

Use cin and extraction operator, >>, to read one or more data
Use cout and insertion operator << to display on the screen

#include <iostream>

int main() {
    // Example of using cin
    int number;
    std::cout << "Enter a number: ";
    std::cin >> number;
    std::cout << "You entered: " << number << std::endl;
    return 0;
}

Question 3

In order to use cin and cout in this format, what do we need to do? (Hint “using”)

Answer 3

Method 1:
using namespace std

Method 2:
using std::cout
using std::cin

Question 4

What do the following math functions in <cmath> do?
sqrt(x)
pow(x, y)
fabs(y)
floor(x)
ceil(x)
exp(x)
log(x)

Answer 4

square root
power
absolute
rounds down to the nearest int
rounds up to the nearest int
exponent
natural log

Question 5

What is the basic format for a reference. Let’s say that the value we want to reference is
int ival = 1024;

Answer 5

int &refVal = ival;

Question 6

Is this following code valid? Why or why not?
int &refval2;

Answer 6

int &refval2; // error, a reference must be initialized.

Question 7

Let’s say that that in main we have
int main() {
int a = 45;
modify(a)
}
void modify(int & x){
x++;
}

What is x called? What is a called? (what’s their names?)

Answer 7

x is a reference and a is called a referent of x.

Question 8

What are the two ways to type explicitly be using the type cast operator in C++?

Answer 8

Method 1:
int x = 4; y = 7;
double ratio = static_cast<double> x/y

Method 2:
int x = 4, y = 7;
double ratio = double(x)/y;

Question 9

Is the following a valid way to initialize a value?

int i(5);

Answer 9

Yes, it is equivalent to
int i = 5;

Question 10

What are the two different ways to initialize a member

Answer 10

Member Initialization
class_name::class_name(value_1, value_2){
	member1 = value_1
	member2 = value_2
}

class_name::class_name(value_1, value_2): member1(value1), member2(value2){
}

Question 11

What is a default constructor. What will happen if you don’t define one? In which cases will C make one for you?

Answer 11

Constructor that has no values passed through. Note that if you don’t define any constructors, C will make one for you. However if you define any constructor you will have to do it yourself.

Question 12

What is the basic format for a getter function? Where do we place the constant?

Answer 12

double get_x()const;
char *get_label()const;

Since getter functions don’t need to change the values, we can add const to the end of the function declaration.

Question 13

What is the correct way to use a pointer to an object?

Answer 13

Point c;
Point *ptr;
ptr = &c;
cout << ptr ->get_x();
cout << (*ptr).get_x();

Question 14

What is the following? 
Point::Point(double a, double b){
x = a;
y=b;

Answer 14

This is a constructor

Question 15

Do constructors have a return type? Can constructors be overloaded

Answer 15

No they don’t have a return type. Yes they can be overloaded

Question 16

What is the :: operator? What does it do? Can several classes have member functions with the same name?

Answer 16

This is the scope resolution operator. It is used to associate a function to its corresponding class.

Yes several classes may have member functions with the same name.

Question 17

What is the general format for the implementation of member functions?

Answer 17

return_type class_name::function_name(parameter_list){
}

Question 18

Which of these is a default constructor, and which isn't?
public:
Point();
Point(double a, double b);

Answer 18

Point(); //default constructor
Point(double a, double b); //non-default

Question 19

What is the return type of a C++ class constructor

Answer 19

depends on the definition of the constructor.

Question 19

True or False?
A class constructor can use the name of the class.

A class have more than one constructor.

Answer 19

Both statements are correct.

Question 20

Let’s say that we have a getter function called get_x() in the class Point.

We then call Point a(6, 7);
How do we print the value of x?

Answer 20

cout << a.get_x() <<endl;

Question 21

What is the difference between private and public members?

Answer 21

Private members can only be accessed by other members. They cannot be directly accessed using the dot operator.

Public members can be accessed from outside the class using the dot operator.

Question 22

True or false, by default all class members are private.

Answer 22

True, all class members are private compared with struct data types where all members are public by default.

Question 23

Where do we place function prototypes in classes?

Answer 23

We place it in public. Example:
class Point {
private:
double x;
double y;
public:
void set_x(double value);
void set_y(double value);
};

Question 24

Is this class definition correct? class Point { private: //some code public: //some code }

Answer 24

No, we are missing the ; at the end. It should be }; at the end.

Question 25

True or false, new creates a block of memory at run time.

Answer 25

True

Question 26

Lets say that we have int *array; How would we allocate memory on the heap for an array with 5 elements? What will be the values stored inside?

Answer 26

array = new int[5]; It will initially be garbage inside.

Question 27

Can we use delete if the space is not allocated or if the space has already been deallocated?

Answer 27

Do not use delete if the space is not allocated or if the space has already been deallocated.

Question 28

How do we delete an array?

Answer 28

Use the delete operator to delete allocated memory by new. delete [] array; Only use [] when referring to an array of built in or user defined types.

Question 29

Will dynamically allocated spaces be deallocated automatically?

Answer 29

No. Therefore a dynamically allocated space should be deallocated by the delete operator,

Question 30

Given this following example, how would we deallocate x and y? Assume that Car is a class Car *x; Car *y; x = new Car; y = new Car[];

Answer 30

``` delete x; delete [] y; ```

Question 31

What is a destructor? Does a destructor have a return value? Can a destructor receive a parameter? Can a destructor be overloaded? When is a destructor called?

Answer 31

A destructor is responsible for resetting the data member values or deallocation of memory. A destructor doesn't return a value and does not receive a parameter. A destructor can NOT be overloaded Destructor will be called automatically when an object goes out of scope. (It can also be called explicitly).

Question 32

Let's say that we have a class called Person. What would the destructor look like if it also has a member name = new char[strlen(n)+1] (essentially saying that name is a character string.

Answer 32

``` Person::~Person(){ delete [] name; name = NULL; } ```

Question 33

What is a default constructor?

Answer 33

A default constructor is when you give the default values if the user provides a null argument. ``` Person::Person(const char *n = NULL, int a = 0{ age = a; name = new char [strlen(n)+1]; assert(n != 0); strcpy(name, n); } ```

Question 34

What is the assert function?

Answer 34

The assert macro checks the given expression. If the expression is false (i.e., the condition is not met), the assert macro outputs a diagnostic message to the standard error stream (typically the console) and terminates the program.

Question 35

In the following example, const char *Student:: get_name() const What does the first const do, and what does the second constant do?

Answer 35

The first const prevents the user from modifying the return value. The second const prevents us from modifying any member variables inside the get_name function.

Question 36

How can we use inline functions? What are inline functions? What are the two methods for implementing inline functions?

Answer 36

If the function body is very short, the overhead of invoking a function call may be too high. In these situations, we can use inline functions. Method 1: int get_value() {return value;} Method 2: inline void decrement (int n) { value -= n; }

Question 37

Can the compiler ignore your request for an inline function? Will a change to an inline function require recompilation of all functions?

Answer 37

The compiler may ignore your request to inline a function Any change to an inline function will require that all functions that call it be recompiled.

Question 38

Can inline functions be recursive? Can inline functions contain an array?

Answer 38

No, inline functions cannot be recursive and cannot contain an array.

Question 39

What are some advantages and disadvantages of inline functions?

Answer 39

Inline functions improve execution times but may increase program size.

Question 40

How could we read characters (including whitespaces). How could we read strings?

Answer 40

``` We can use get() to read any character and getline() to read strings. char ch ch = cin.get(); string name; getline (cin, name); get example std::cin.get(ch); std::cout << "You entered: " << ch << std::endl; getline example std::getline(std::cin, line); std::cout << "You entered: " << line << std::endl; ```

Question 41

How could we format output for fixed, scientific or setting precision to let's say 2?

Answer 41

First we need to include cout<

Question 42

How could we set the field size to display a value of x in a field of 10? double x = 61110.56673

Answer 42

``` double x = 61110.56673 cout<> i; cout << "Please enter a character "; cin >> ch; return 0;

No it will not read a character. This is because cin will consume just enough characters to do its job. The solution: char ch; cin.clear(); do { ch = cin.get(); //reads a character } while (ch != '\n' && ch!= EOF);

Question 45

Let's say that we have a constructor Person Person::Person(const char *n, int a) We wish the save n into a member called name. How would we do that assignment. Let's also say that we want to do this dynamically on the heap.

Answer 45

name = new char [strlen(n)+1]; Note that we add 1 since we need to add the \0.

Question 46

Which of the following is a call to the constructor? MyString s1("World"); MyString s2 = s1;

Answer 46

MyString s1("World"); //this is a call to the constructor. MyString s2 = s1; This is not a call. This is initialization.

Question 47

What are the issues with something like MyString s2 = s1;

Answer 47

S2 is not a real copy of s1. They point to the same place on the heap. The destructor of MyString will be called twice when s1 and s2 go out of scope. The destructor will attempt to deallocate the storage twice leading to a possible segmentation fault.

Question 48

How would we define a copy constructor. Assume the class is called MyString and we want to copy over strings.

Answer 48

MyString::MyString(const MyString &s): lengthM(s.lengthM) { storageM = new char[lengthM+1]; assert(storageM != 0); strcpy(storageM, s.storageM); }

Question 49

How do we format a strcpy?

Answer 49

char *strcpy(char *dest, const char *src);

Question 50

''' Is the following inline function correct? int get_value() {return_value}; '''

Answer 50

No. The semi colon is in the wrong place. It should be int get_value() {return value;}