Review Questions
5.1 How do structures in C and C++ differ?
Answer:
C structure member functions are not permitted but in C++ member functions are permitted.
5.2 What is class? How does it accomplish data hiding?
Answer:
A class is a way to bind the data and its associated functions together.
In class, we can declare data as private so that the functions outside the class can not access the data and thus accomplish data hiding.
5.3 How does a C structure differ from a C++ class?
Answer:
Initially (in C) a structure was used to bundle different data types together to perform a particular functionality C++ extended the structure to contain functions. The difference is that all declarations inside a structure are default public.
5.4 What are objects? How are they created?
Answer:
Object is a member of class.
Simple example:
class fruit
{
… …
};
We can create an object as follows:
fruit mango;
here mango is an object.
5.5 How is a member function of a class defined?
Answer:
Member function of a class can be defined in two places:
- Inside the class definition: same as other normal function.
- Outside the class definition: general form:
return-type class-name: function-name(argument list)
{
function body
}
5.6 Can we use the same function name for a member function of a class and an outside function in the same program file? If yes, how are they distinguished? If no, give reasons.
Answer:
Yes, we can distinguish them during calls to main() function. The following example illustrates this:
#include<iostream>
using namespace std;
void func()
{cout << "Outside of Class \n";
}class sunny
{
public:void func(){cout << "Inside of Class \n";}
};int main()
{func(); // outside func() is calling.sunny ruby;ruby.func(); // inside func() is calling.return 0;
}
5.7 Describe the mechanism of accessing data members and member functions in the following case:
a. Inside the main program.
b. Inside a member function of the same class.
c. Inside a member function of another class.
Answer:
a. Using object and dot membership operator.
b. Just like accessing a local variable of a function.
c. Using object and dot dembership operator.
The following exampleexplains how to access data members and member functions inside a member function of another class.
#include<iostream>
using namespace std;
class a
{
public:int x;void display(){cout << "This is class a \n";x = 111;}
};class b
{
public:void display(){a s;cout << "Now member function 'diaplay()' of class a is calling from class b \n";s.display();cout << " x = " << s.x <<"\n";}
};int main()
{b billal; // billal is a object of class b.billal.display();return 0;
}
5.8 When do we declare a member of a class static?
Answer:
We can define class members as static using static keywords. When we declare a member of a class as static it means no matter how many objects of the class are created, there is only one copy of the static member.
A static member is shared by all objects of the class. All static data is initialized to zero when the first object is created if no other initialization is present. We can’t put it in the class definition but it can be initialized outside the class, using the scope resolution operator :: to identify which class it belongs to.
5.9 What is a friend function? What are the merits and demerits of using friend functions?
Answer:
A function that acts as a bridge among different classes, then it is called friend function.
Merits:
We can access the other class members in our class if we use friend keyword;
We can access the members without inheriting the class.
Demerits:
The maximum size of the memory will occupied by objects according to the size of friend members.
5.10 State whether the following statements are TRUE or FALSE.
a. Data item in a class must always be private.
b. A function designed as private is accessible only to member functions of that class.
c. A function desigened as public can be accessed like any other ordinary functions.
d. Member functions defined inside a class specifier become inline functions by default.
e. Classes can bring together all aspects of an entity in one place.
f. Class members are public by default.
g. Friend functions have access to only public members of a class.
h. An entire class can be made a friend of another class.
i. Functios cannot return class object.
j. Data members can be initialized inside class specifier.
Answer:
a. FALSE
b. TRUE
c. FALSE, A function desigened as public can be accessed like any other ordinary functions from the member function of the same class.
d. TRUE
e. TRUE
f. FALSE
g. FALSE
h. TRUE
i. FALSE
j. FALSE
Debugging Exercises
5.1 Identify the error in the following program.
#include<iostream>
using namespace std;
class Room
{int width;int length;void setValue(int w, int l){width = w;length = l;cout << "Width is : " << width << ", Length is : " << length << endl;}
};int main()
{Room objRoom;objRoom.setValue(12, 1.4);return 0;
}
Answer:
Because “Room” is defined as “class” then the function “void setValue(int w, int l)” must be public.
If defined Room as “struct”, then there is no error.
5.2 Identify the error in the following program.
#include<iostream>
using namespace std;
class Item
{private:static int count;public:Item(){count++;}int getCount(){return count;}int * getCountAddress(){return count;}
};int Item::count = 0;int main()
{Item objItem1;Item objItem2;cout << objItem1.getCount() << ", ";cout << objItem2.getCount() << ", ";cout << objItem1.getCountAddress() << ", ";cout << objItem2.getCountAddress() << ", ";return 0;
}
Answer: invalid conversion from ‘int’ to ‘int*’ - > Correction
int * getCountAddress()
{return &count;
}
All other code remain unchanged.
5.3 Identify the error in the following program.
#include<iostream>
using namespace std;
class staticfunction
{static int count;public:static void setCount(){count++;}void displayCount(){cout << count;}
};int staticfunction::count = 10;int main()
{staticfunction obj1;obj1.setCount(5);staticfunction::setCount();obj1.displayCount();return 0;
}
Answer:
setCount() is not accept parameter, so here obj1.setCount(5); replace with obj1.setCount();
5.4 Identify the error in the following program.
#include<iostream>
using namespace std;
class Length
{int feet;float inches;public:Length(){feet = 5;inches = 6.0;}Length(int f, float in){feet = f;inches = in;}Length addLength(Length l){l.inches; this->inches;l.feet += this->feet;if(l.inches > 12){l.inches -= 12;l.feet++;}return l;}int getFeet(){return feet;}float getInches(){return inches;}
};int main()
{Length objLength1;Length objLength1(5, 6.5);objLength1 = objLength1.addLength(objLength2);cout << objLength1.getFeet() << ", ";cout << objLength1.getInches() << " ";return 0;
}
Answer:
In the main() function ‘objLength2’ was not declared in this scope.
Correction:
Length objLength1(5, 6.5); -> Length objLength2(5, 6.5);
Programming Exercises
5.1 Define a class to represent a bank account. Include the following members:
Data members:
Name of the depositor;
Account number;
Type of account;
The balance amount in the account.
Member functions:
To assign initial values.
To deposit an amount.
To withdraw an amount after checking the balance.
To display the name and balance.
Write a main program to test the program.
Answer:
#include <iostream>
#include <iomanip>
using namespace std;class bank
{private:string name;int acc_Nr;string acc_Type;double balance;public:int assign();void deposit(float b);void withdraw(float c);void display();};int bank::assign()
{float initial;cout << "You have to pay 100Euro to open your account \n"<< "You have to store at least 200 Euro to keep account active. \n"<< "Would you want to open a account? \n"<< "If Yes press 1 \n"<< "If No press 0 \n";int test;cin >> test;if(test == 1){initial = 200;balance = initial;cout << "Enter your name, account number & account type to create account : ";cin >> name >> acc_Nr >> acc_Type;}else;return test;
}void bank::deposit(float b)
{balance += b;
}void bank::withdraw(float c)
{balance -= c; // withdrawif(balance < 200){cout << "Sorry, your balance is not sufficient to withdraw " << c << "Euro.\n"<< "You have to store at least 200 Euro to keep your account active.\n";balance += c;}
}void bank::display()
{cout << setw(12) << "Name" << setw(20) << "Account Type" << setw(12) << "Balance" << endl;cout << setw(12) << name << setw(20) << acc_Type << setw(12) << balance << endl;
}int main()
{bank account;int t;t = account.assign(); // initializationif(t == 1){cout << "Would you want to deposite ?" << endl<< "If NO press 0(zero)" << endl<< "If Yes enter deposite ammount : "<< endl;float dp;cin >> dp;account.deposit(dp);cout << "Would you want to withdraw ?"<< endl<< "If NO press 0(zero)" << endl<< "If Yes enter withdraw ammount : "<< endl;float wd;cin >> wd;account.withdraw(wd);cout << " See details :" << endl << endl;account.display();}else if(t == 0)cout << "Thank you! \n";return 0;
}
5.2 Write a class to represent a vector (a series of float values). Include member functions to perform the following tasks:
a. To create the vector
b. To modify the value of a given element
c. To multiply by a scalar value.
d. To display the vector in the form(10, 20, 30, …)
Answer:
#include <iostream>
#include <iomanip>
using namespace std;class vector
{private:float *fp;int size;public:void creat_vec(int a);void set_element(int i, float value);void modify_vec();void multiply(float b);void display_vec();};void vector::creat_vec(int a)
{size = a;fp = new float[size];
}void vector::set_element(int i, float value)
{fp[i] = value;
}void vector::multiply(float b)
{for(int i=0; i<size;i++){fp[i] = b * fp[i];}
}void vector::display_vec()
{cout << "fp[" << size << "] = (";for(int j=0;j<size;j++){if(j == size-1)cout << fp[j];elsecout << fp[j] << " , ";}cout << ")" << endl;
}void vector::modify_vec()
{int i;cout << " to edit a given element enter position of the element : ";cin>>i;i--;cout << " Now enter new value of " << i+1 << "th element : ";float v;cin>>v;fp[i] = v;cout << "Now new contents : " << endl;display_vec();cout << " to delete an element enter position of the element : ";cin>>i;i--;for(int k=i;k<size;k++){fp[k] = fp[k+1];}size--;cout<< "New contents : "<<endl;display_vec();
}int main()
{vector sunny;int s;cout << "Enter size of vector : ";cin>>s;sunny.creat_vec(s);cout << "enter " << s << " elements one by one : " << endl;for(int n=0;n<s;n++){float v;cin>>v;sunny.set_element(n,v);}cout << "Npw contents : " << endl;sunny.display_vec();cout << "to multiply this vector by a scalar quantity enter this scalar : ";float m;cin>>m;sunny.multiply(m);cout << "New contents : " << endl;sunny.display_vec();sunny.modify_vec();return 0;
}
5.3 Modify the class and the program of Exercise 5.1 for handling 10 customers.
Answer:
#include <iostream>
#include <iomanip>
using namespace std;
#define size 10
char* serial[size] = {"1st", "2nd", "3rd", "4th", "5th", "6th", "7th", "8th", "9th", "10th"};class bank
{private:string name;int acc_Nr;string acc_Type;double balance;public:int assign();void deposit(float b);void withdraw(float c);void displayon();void displayoff();};int bank::assign()
{float initial;cout << "You have to pay 100Euro to open your account \n"<< "You have to store at least 200 Euro to keep account active. \n"<< "Would you want to open a account? \n"<< "If Yes press 1 \n"<< "If No press 0 \n";int test;cin >> test;if(test == 1){initial = 200;balance = initial;cout << "Enter your name, account number & account type to create account : ";cin >> name >> acc_Nr >> acc_Type;}else;return test;
}void bank::deposit(float b)
{balance += b;
}void bank::withdraw(float c)
{balance -= c; // withdrawif(balance < 200){cout << "Sorry, your balance is not sufficient to withdraw " << c << "Euro.\n"<< "You have to store at least 200 Euro to keep your account active.\n";balance += c;}
}void bank::displayon()
{cout << setw(12) << name << setw(20) << acc_Type << setw(12) << balance << endl;
}void bank::displayoff()
{cout << " Account has not created !" << endl;
}int main()
{bank account[size];int t[10];for(int i=0;i<size;i++){cout << "Enter information for " << serial[i] << "customer : " << endl;t[i] = account[i].assign();if(t[i] == 1){cout << "Would you want to deposite ?" << endl<< "If NO press 0(zero)" << endl<< "If Yes enter deposite ammount : "<< endl;float dp;cin >> dp;account[i].deposit(dp);cout << "Would you want to withdraw ?"<< endl<< "If NO press 0(zero)" << endl<< "If Yes enter withdraw ammount : "<< endl;float wd;cin >> wd;account[i].withdraw(wd);cout << endl << endl;}else if(t[i] == 0)cout << "Thank you! \n";}cout << " See details :" << endl << endl;cout << setw(12) << "Name" << setw(20) << "Account Type" << setw(12) << "Balance" << endl;for(int j=0;j<size;j++){if(t[j] == 1)account[j].displayon();else if (t[j] == 0)account[j].displayoff();}return 0;
}
5.4 Modify the class and the program of Exercise 5.2 such that the program would be able to add two vectors and display the resultant vector.(Note that we can pass objects as function arguments)
Answer:
#include <iostream>
#include <iomanip>
using namespace std;class vector
{private:float *fp;int size;public:void creat_vec(int a);void set_element(int i, float value);friend void add_vec(vector, vector, int n);};void vector::creat_vec(int a)
{size = a;fp = new float[size];
}void vector::set_element(int i, float value)
{fp[i] = value;
}void add_vec(vector v1, vector v2, int sz)
{float *sum;cout << "sum[" << sz << "] = (";sum = new float[sz];for(int i=0;i<sz;i++){sum[i] = v1.fp[i] + v2.fp[i];if(i == sz-1)cout << sum[i];elsecout << sum[i] << " , ";}cout << ")" <<endl;
}int main()
{vector x1, x2;int s;cout << "Enter vector's size : ";cin>>s;cout << "Enter " << s << " elements of FIRST vector : ";x1.creat_vec(s);x2.creat_vec(s);for(int j=0;j<s;j++){float v;cin>>v;x1.set_element(j,v);}cout << "Enter " << s << " elements of SECOND vector (Two vector MUST have the SAME size): ";for(int i=0;i<s;i++){float r;cin>>r;x2.set_element(i,r);}add_vec(x1, x2, s);return 0;
}
5.5 Creat two classes DM and DB which store the value of distances. DM stores distances in meters and centimeters and DB in feet and inches. Write a program that can read values for the class objects and add one object of DM with another object of DB.
Use a friend function to carry out the addition operation. The object that stores the resultsmay be a DM object or DB object, depending on the units in which the results are required.
The display should be in the format of feet and inches or meters and centimeters depending on the object on display.
Answer:
#include <iostream>
#include <iomanip>
using namespace std;
# define factor 0.3048
class DB;class DM
{float d;public:void store(float x) {d = x;}friend void sum(DM, DB);void show();
};void DM::show()
{cout << "\n Distance = " << d << " meter or " << d * 100 << " centimeter \n";
}class DB
{float l;public:void store(float y) {l = y;}friend void sum(DM, DB);void show();
};void DB::show()
{cout << "\n Distance = " << l << " feet or " << l * 12 << " inches \n";
}void sum(DM m, DB b)
{float sum;sum = m.d + b.l * factor;float f;f = sum / factor;DM m1;DB b1;m1.store(sum);b1.store(f);cout << " Press 1 to diaplay result in meter \n"<< " Press 2 to display result in feet \n"<< " What is your option ? : ";int test;cin >> test;if(test == 1)m1.show();else if(test == 0)b1.show();
}int main()
{DM dm;DB db;dm.store(10.5);db.store(12.3);sum(dm, db);return 0;
}
