Applications of Container Class: Vectors, Stack, List, Map

Applications of Container Class

1. Vectors

 

• Vector is a most general purpose container. It stores the elements in contiguous memory locations. Any element of vector can be accessed directly using index of it given by subscript operator [ ]. It supports the dynamic array. The dynamic array is an array which can grow or shrink dynamically. The memory allocation for vector is done at the run time.

• The vector can be declared as

vector <int> v; //It creates a zero length vector

vector<char> v(5);//creates the vector with 5 element character.

vector <double> v2(v1)//creates v2 vector from v1 vector of double type.

vector <char> v(4, 'a')//initializes 4 element char vector

• In the program we have to include header file <vector> in the program. The program for vector implementation is as illustrated below ‒

#include <iostream>

#include <vector>

using namespace std;

int main()

{

vector<char> v(10); // create a vector of length 10.

int i;

// display size of vector

cout << "The size of vector = " << v.size() << endl;

//store English alphabets to vector

for(i=0; i<10; i++)

   v[i] = i + 'A';

// display contents of vector

cout<<"Elements in the vector are:\n";

for(i=0; i<v.size(); i++)

   cout << v[i] <<< " ";

cout << "\n\n";

cout << "Inserting more elements to vector..."<<endl;

for(i=0; i<5; i++)

   v.push_back(i + 10 + 'A');//vector grows

// display size of vector

cout << "New size of vector = "<< v.size() << endl;

// display contents of vector

cout<<"Elements in vector are:\n";

for(i=0; i<v.size(); i++)

   cout << v[i] << " ";

cout << "\n\n";

//deleting last five elements of the list

Standard Template Library

cout<<"\n Now deleting the 5 elements from end of the vector..."<<endl;

for(i=0;i<5;i++)

   v.pop_back();//vector shrinks

cout<<"\n";

//Retaining the original list

cout << "Elements in vector are:\n";

for(i=0; i<v.size(); i++)

   cout << v[i] << " ";

cout<<"\n\n";

cout<<"The size is now = "<<v.size();

cout << "\n\n";

retrun 0;

}

Output

The size of vector = 10

Elements in the vector are:

A B C D E F G H I J

Inserting more elements to vector...

New size of vector = 15

Elements in vector are:

A B C D E F G H I J K L M N O

Now deleting the 5 elements from end of the vector...

Elements in vector are:

A B C D E F G H I J

The size is now = 10

Program explanation

• In above program we have declared the char vector of length 10 as

vector<char> v(10);

• The vector function v.size() is used to obtain the size of the vector. Then we inserted some characters in the vector by v.push_back function. By this function we can insert the element at the end of the vector, i.e. we have inserted 5 elements after 'A'+10 elements. In other words we have inserted (K, L, M, N and O after J). Again by using v.size() we can obtain the modified size of vector.

• Using v.pop_back() we have deleted the last five elements and retain the original vector.

• Thus the above program of vector is for expanding and shrinking the vector.

• Some commonly used vector functions are ‒

Function   ‒    Description

begin() ‒  Returns the first element of the vector.

end() ‒  Returns the last element of the vector.

size() ‒  Returns the size of the vector.

erase() ‒  Erases the given elements.

push_back() ‒  Insert the element in the vector at the end.

pop_back()  ‒  Deletes the last element of the vector.

resize() ‒   Modifies the original size of the vector.

 

Example : 1

Create a vector named Student to add names of the students in a class. Also display the contents of the vector after adding necessary elements.

Solution :

#include<iostream>

#include <string>

#include <vector>

using namespace std;

class Student

{

   string myName, myStudentID, myCourse;

   public:

   Student(string name, string studentID, string course)

   {

      myName = name;

      myStudentID studentID;

      myCourse = course;

   }

   void display()

   {

      cout << "\n" << myName << "\t" << myStudentID << "\t" << myCourse;

   }

};

int main()

{

   int n;

   vector<Student> studentList;

   cout<<"Enter Total number of students << endl;

   cin >> n;

   for (int i = 0; i < n; i++)

   {

      string inputName, inputStudentID, inputCourse;

      cout<<"Enter Student name: ";

      cin>>inputName;

      cout << "Enter Student ID : ";

      cin>>inputStudentID;

      cout << "Enter Course Name: ";

      cin>>inputCourse;

      Student obj(inputName, inputStudentID, inputCourse);

      studentList.push_back(obj);

      cout << endl;

  }

  cout << "The student list has a size of " << studentList.size() << endl;

  cout << "Name \t ID \t Course";

  for (int i = 0; i < n; i++)

  {

        studentList[i].display();

  }

  cout << endl;

  return 0;

}

Output

Enter Total number of students

3

Enter Student name: AAA

Enter Student ID: 10

Enter Course Name: Computer

Enter Student name: BBB

Enter Student ID: 20

Enter Course Name: Electrical

Enter Student name : CCC

Enter Student ID: 30

Enter Course Name: E&TC

The student list has a size of 3

Name      ID       Course

AAA      10        Computer

BBB       20        Electrical

CCC       30        E&TC

 

2. Stack

 

• The stack is a LIFO data structure. That means the element inserted at the last gets popped off first. The basic operations that can be implemented on stack are –

1. Push

2. Pop

• Before popping the element it is necessary to check whether the stack is empty or not. Hence stack empty operation is also an important operation.

• Stack is a derived container class which is basically derived from the sequence container deque.

• Following is a list of operations that are supported by the stack derived container class.

Function  ‒      Meaning

push(item) ‒ This function helps to push an item onto the stack.

pop()  ‒ This function pops the topmost element from the stack.

size() ‒ This function returns the size of the stack.

top() ‒ This function returns value which is at the top of the stack.

• For using these functions in the program we must include the header file <stack> at the top. Following is a simple C++ program in which the derived container class stack is used. Various operations are also performed on this stack using the inbuilt functions of container class library.

#include<iostream>

#include<stack> //header file stack must be included

using namespace std;

int main()

{

stack<int> s; //object is created for stack class

//Note that this class handles the int values

int item;

char ans;

int choice;

do

{

    cout<<"\n Main Menu";

    cout<<"\n 1.Push ";

    cout<<"\n 2.Pop ";

    cout<<"\n 3.Display ";

    cout<<"\n Enter your choice ";

    cin>>choice;

    switch(choice)

    {

        1: cout<<"\n Enter the element to be pushed ";

        cin>>item;

        s.push(item);//pushing the element onto the stack

        cout<<"\n Item is pushed!!!";

        break;

        case 2: if(!s.empty())//checking stack is empty or not

        {

            s.pop();//popping the element from the stack

            cout<<"\n Popped an item!!!";

        }

        else

            cout<<"\n stack empty!!!";

        break;

        case 3:if(ls.empty())

        {

            cout<<"Top element of the stack is "<<s.top();  // Displaying the stack top element

        }

        else

            cout<<"\n The stack is empty!!!";

        break;

    }

cout<<"\n Do you want to continue?

cin>>ans;

}while(ans= ='y');

return 0;

}

Output

Main Menu

1.Push

2.Pop

3.Display

Enter your choice 1

Enter the element to be pushed 10

Item is pushed!!!

Do you want to continue? y

Main Menu

1.Push

2.Pop

3.Display.

Enter your choice 1

Enter the element to be pushed 20

Item is pushed!!!

Do you want to continue? y

Main Menu

1.Push

2.Pop

3.Display

Enter your choice 1

Enter the element to be pushed 30

Item is pushed!!!

Do you want to continue? y

Main Menu

1.Push

2.Pop

3.Display

Enter your choice 3

Top element of the stack is 30

Do you want to continue? y

Main Menu

1.Push

2.Pop

3.Display

Enter your choice 2

Popped an item!!!

Do you want to continue? y

Main Menu

1.Push

2.Pop

3.Display

Enter your choice 3

Top element of the stack is 20

Do you want to continue? y

Main Menu

1.Push

2.Pop

3.Display

Enter your choice 2

Popped an item!!!

Do you want to continue? y

Main Menu

1.Push

2.Pop

3.Display

Enter your choice 3

Top element of the stack is 10

Do you want to continue? y Main Menu

1.Push

2.Pop

3.Display

Enter your choice 2

Popped an item!!!

Do you want to continue? y

Main Menu

1.Push

2.Pop

3.Display

Enter your choice 3

The stack is empty!!!

Do you want to continue? y

Main Menu

1.Push

2.Pop

3.Display

Enter your choice 2

stack empty!!!

Do you want to continue?n

 

3. List

 

• List is a collection of elements in which only sequential access to the elements is allowed. This is basically a bidirectional linear list in which we can traverse the elements from left to right and from right to left. As bidirectional traversing is possible the insertion and deletion of elements is efficient.

• The header file <list> needs to be included in the program.

#include <iostream>

#include <list>

using namespace std;

int main()

{

list<int> lst; // create an empty list

int i,n,item;

//storing the elements in the list

cout <<"\n How many elements you want to insert?"<<endl;

cin>>n;

cout<<"\n Enter the Elements in the List"<<endl;

for(i=0; i<n; i++)

{

    cin>>item;

    1st.push_back(item);

}

cout << "The size of list is = " << 1st.size() << endl;

//displaying the contents of the list

cout << “The contents of the List are: "<<endl;

list<int>::iterator ptr = lst.begin();

while(ptr ! = 1st.end())

{

    cout << ptr << " ";//accessing the contents through iterator

    ptr++;

}

//sorting the contents of the list

1st.sort();

//displaying the sorted list

cout << "\n\n Sorted elements of the List are: "<<endl;

ptr = 1st.begin();

while(ptr ! = 1st.end())

{

    cout << *ptr << " ";

    ptr++;

}

// Modifying the List

ptr =1st.begin();

while(ptr != 1st.end())

{

    *ptr *ptr + 1000;

    ptr++;

}

//displaying the modified list using iterator

cout << "\nModified elements of the list are: "<<endl;

ptr = 1st.begin();

while(ptr = lst.end())

{

    cout << *ptr << " ";

    ptr++;

}

cout<<"\n\n";

return 0

}

Output

How many elements you want to insert?

5

Enter the Elements in the list

30

10

20

40

50

The size of list is = 5

The contents of the List are:

30 10 20 40 50

Sorted elements of the list are:

10 20 30 40 50

Modified elements of the list are:

1010 1020 1030 1040 1050

Program explanation

• In above given program, initially the empty list is created by

list<int> lst;

• Then using the push_back() function we have inserted the elements in the list

for(i=0; i<n; i++)

{

      cin>>item;

      1st.push_back(item);

}

• One iterator is declared and initialized and using which we are trying to access the contents of the list as follows ‒

list<int>::iterator ptr = lst.begin();

• The iterator is given by pointer ptr. The following code is for accessing the contents of the list.

while(ptr != 1st.end())

{

    cout << *ptr << " ";

    ptr++;

}

• The list can be sorted simply by invoking Ist.sort() function.

• Various commonly used functions of list are given in following table ‒

Function  ‒   Description

begin() ‒  Returns the first element of the list.

end() ‒   Returns the last element of the list.

size() ‒    Returns the size of the list.

pop_back() ‒   Removes last element of the list.

pop_front() ‒   Removes the first element of the list.

push_back() ‒    Inserts the specified value at the end of the list.

push_front() ‒    Inserts the specified value at the beginning of the list.

reverse() ‒    Reverses the list.

sort()  ‒     Sort the contents of the list.

 

4. Map

 

• The map is an associative container in which the elements are stored in the form of key value and mapped value. For example ‒ {(1, a), (2, b), (3, c)}

• In a map, the key values are generally used to sort and uniquely identify the elements, while the mapped values store the content associated to this key. The types of key and mapped value may differ.

• The duplicate values are not allowed in map. Hence it possess one to one relationship.

• The header file <map> is included in the program for creating and using the map object.

• The key value and the mapped value are grouped together in member type value_type which is a pair type as

typedef pair<const Key, T> value_type;

• The syntax for creating map is,

map<key,value> map name

• Various operations that can be performed on map are ‒

Function name   ‒   Purpose

insert(pair) ‒ The element is inserted into the map.

erase(iterator i) ‒ The element pointed by the iterator is deleted from the map.

void swap(map) ‒ Swaps the contents of the map.

void clear()‒ Clears the contents.

 size_type size()‒ Returns the size of the container.

 

• The C++ program is as follows

#include <iostream>

#include <map>

using namespace std;

int main()

{

int count,key;

char ans = 'y',item;

int choice;

map<int,char> m;

map<int,char>::iterator i;

do

{

    cout<<"\n Program for Implementing MAP using Associative Container";

    cout << "\n Main Menu";

    cout << "\n1. Insert an element";

    cout << "\n2. Delete an element";

    cout << "\n3. Get the Size of MAP";

    cout << "\n4. Search an element";

    cout<<"\n5. Display";

    cout<<"\n Enter your choice: ";

    cin>> choice;

    switch (choice)

    {

        case 1:cout << "\n Enter the element the key: ";

           cin >> key;

            cout << "\n Enter the value to be inserted: ";

            cin>> item;

            m.insert(pair<int,char>(key,item));

            break;

        case 2:cout << "\n Enter the key to be deleted: ";

            cin >> key;

            m.erase(key);

            break;

        case 3:count = m.size();

            cout << "\n The size of set is: <<< count;

            break;

        case 4:cout << "\n Enter the Key at for searching the element: ";

            cin>> key;

            if(m.count(key)!=0) // first represents key and second represents value

            cout << "Element" << m.find(key)‒>second << " is present" << endl;

            else

            cout << "Element is not present" << endl;

            break;

        case 5:cout << "Elements of MAP are: ";

            for (i = m.begin(); i != m.end(); i++)//i is for iterator

                cout <<"[" <<(*i).first << ", "<<(*i).second<<"]";

}

cout << "\n Do you want to continue?(y/n): ";

cin >> ans;

} while (ans == 'y' || ans == 'Y');

}

Output

Program for Implementing MAP using Associative Container

Main Menu

1. Insert an element

2. Delete an element

3. Get the Size of MAP

4. Search an element

5. Display

Enter your choice: 1

Enter the element the key: 1

Enter the value to be inserted: a

Do you want to continue?(y/n): y

Program for Implementing MAP using Associative Container

Main Menu

1. Insert an element

2. Delete an element

3. Get the Size of MAP

4. Search an element

5. Display

Enter your choice: 1

Enter the element the key: 2

Enter the value to be inserted: b

Do you want to continue?(y/n): y

Program for Implementing MAP using Associative Container

Main Menu

1. Insert an element

2. Delete an element

3. Get the Size of MAP

4. Search an element

5. Display

Enter your choice: 1

Enter the element the key: 3

Enter the value to be inserted: c

Do you want to continue?(y/n); y

Program for Implementing MAP using Associative Container

Main Menu

1. Insert an element

2. Delete an element

3. Get the Size of MAP

4. Search an element

5. Display

Enter your choice: 1

Enter the element the key: 4

Enter the value to be inserted: d

Do you want to continue?(y/n): y

Program for Implementing MAP using Associative Container

Main Menu

1. Insert an element

2. Delete an element

3. Get the Size of MAP

4. Search an element

5. Display

Enter your choice: 5

Elements of MAP are: [1, a] [2, b] [3, c] [4, d]

Do you want to continue?(y/n): y

Program for Implementing MAP using Associative Container

Main Menu

1. Insert an element

2. Delete an element

3. Get the Size of MAP

4. Search an element

5. Display

Enter your choice: 2

Enter the key to be deleted: 3

Do you want to continue?(y/n): y

Program for Implementing MAP using Associative Container

Main Menu

1. Insert an element

2. Delete an element

3. Get the Size of MAP

4. Search an element

5. Display

Enter your choice: 5

Elements of MAP are: [1, a] [2, b] [4, d]

Do you want to continue?(y/n): y

Program for Implementing MAP using Associative Container

Main Menu

1. Insert an element

2. Delete an element

3. Get the Size of MAP

4. Search an element

5. Display

Enter your choice: 3

The size of set is: 3

Do you want to continue?(y/n): y

Program for Implementing MAP using Associative Container

Main Menu

1. Insert an element

2. Delete an element

3. Get the Size of MAP

4. Search an element

5. Display

Enter your choice: 4

Enter the Key at for searching the element: 2

Element b is present

Do you want to continue?(y/n): n

 

Example : 2

Implement a Dictionary named "Index" which consists of Key terms and its Description using MAP STL. Try to display all the terms and descriptions present in the dictionary and if a key term has been provided as an input, the corresponding description should get displayed as an output to the user by searching the entire dictionary.

Solution :

#include <iostream>

#include<string>

#include <map>

using namespace std;

int main()

{

string key,item;

char ans = 'y';

int choice;

map<string, string> Index;

map<string, string>::iterator i;

do

{

    cout << "\n Main Menu";

    cout<<"\n1. Insert an element";

    cout<<"\n2. Search an element";

    cout << "\n3. Display";

    cout << "\n Enter your choice: ";

    cin>> choice;

    switch (choice)

    {

        case 1:cout << "\n Enter the word: ";

            cin >> key;

            cout<<"\n Enter its meaning: ";

            cin >> item;

            Index.insert(pair<string, string>(key, item));

            break;

        case 2:cout << "\n Enter the word for finding its meaning: ";

            cin >> key;

            if (Index.count(key) != 0) // first represents key and second represents value

                cout << "Meaning is: " << Index.find(key)‒>second << endl;

            else

                cout << "Word is not present" << endl;

            break;

        case 3:cout << "Words in Dictionary: ";

            for (i = Index.begin(); i != Index.end(); i++)//i is for iterator

                cout << "I" << (*i).first << ", " << (*i).second << "] ";

        }

cout << "\n Do you want to continue?(y/n): ";

cin >> ans;

} while (ans = = 'y' || ans = = 'Y');

}

Output

Main Menu

1. Insert an element

2. Search an element

3. Display

Enter your choice: 1

Enter the word: attempt

Enter its meaning: try

Do you want to continue?(y/n): y

Main Menu

1. Insert an element

2. Search an element

3. Display

Enter your choice: 1

Enter the word: ability

Enter its caning: capacity

Do you want to continue?(y/n): y

Main Menu

1. Insert an element

2. Search an element

3. Display

Enter your choice: 1

Enter the word: bad

Enter its meaning: awful

Do you want to continue?(y/n): y

Main Menu

1. Insert an element

2. Search an element

3. Display

Enter your choice: 1

Enter the word: calm

Enter its meaning: quiet

Do you want to continue?(y/n): y

Main Menu

1. Insert an element

2. Search an element

3. Display

Enter your choice: 1

Enter the word: dominant

Enter its meaning: Superior

Do you want to continue?(y/n); y

Main Menu

1. Insert an element

2. Search an element

3. Display

Enter your choice: 3

Words in Dictionary: [ability, capacity] [attempt, try] [bad, awful] [calm, quiet] [dominant, Superior]

Do you want to continue?(y/n): y

Main Menu

1. Insert an element

2. Search an element

3. Display

Enter your choice: 2

Enter the word for finding its meaning: calm

Meaning is: quiet

Do you want to continue?(y/n):

 

Review Question

1. Explain how the stack can be implemented using STL.