Example to show the difference between struct and class in C++

This is a very simple example showing the difference between struct and class in C++. In reality there is hardly any difference between struct and class in C++. They are exactly the same except that the default is public in struct and private in class. You can do everything you can do in a class in a struct but its not a good practice. The reason being struct's are inherited from C programming and as the name suggests it was meant to represent a structure. You can also read the C++ FAQ that explains it better.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This very simple example demonstrates the basic difference 
//between struct and class in C++

#include<iostream>

using namespace std;

class A {
  int a; //default in class is private

public:
  int b;
  void initVariables(int c1, int c2, int c3)
  {
    a=c1, b=c2, c=c3;
  }
  void printVariables()
  {
    cout<<"a = "<<a<<"    b = "<<b<<"    c = "<<c<<endl;
  }

private:
  int c;
};

struct B {
  int a; //default in struct is public

public:
  int b;
  void initVariables(int s1, int s2, int s3)
  {
    a=s1, b=s2, c=s3;
  }
  void printVariables()
  {
    cout<<"a = "<<a<<"    b = "<<b<<"    c = "<<c<<endl;
  }

private:
  int c;
};

int main()
{
  A var1;
  var1.initVariables(10, 11, 12);
  //var1.a = 15; //Cant be changed as its private
  var1.b = 16;
  //var1.c = 17; //Cant be changed as its private
  cout<<"Printing the variables from the class"<<endl;
  var1.printVariables();

  B var2;
  var2.initVariables(20, 21, 22);
  var2.a = 25; //possible
  var2.b = 26;
  //var2.c = 27; //Cant be changed as its private
  cout<<"\n\nPrinting the variables from the struct"<<endl;
  var2.printVariables();
  cout<<"\n\n";

  return 0;
}

The output is as follows:

Example of Virtual Functions

The following is a simple example of Virtual functions. There is a Shape class which is the base class and three other classes are derived from the Shape class. The Circumference method in the base class is 'pure virtual' so it has to be defined in the derived classes else the compiler will complain about the class being abstract. Note that even if a base class has a single pure virtual function, it would become as an Abstract Base class.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This shows an example of C++ virtual function/methods
//This example also covers a pure virtual method
//This also shows an example of Inheritance
#include<iostream>

using namespace std;

//Base Class
class Shape {
public:
  virtual void Area(int length, int breadth)
  {
    cout<<"Shape: Area = "<<length * breadth<<endl;
  }
  virtual void Circumference(int length, int breadth) = 0; //pure virtual
};

//Derived class - Inherits Shape as Public
class Rectangle : public Shape {
public:
  void Circumference(int length, int breadth)
  {
    cout<<"Rectangle: Circumference = "<<2*(length + breadth)<<endl;
  }
};

//Derived class - Inherits Shape as Public
class Square : public Shape {
public:
  //Overloaded Area because for Square length = breadth
  void Area(int length)
  {
    Shape::Area(length, length);
  }
  //Overloaded Circumference because for Square length = breadth
  void Circumference(int length)
  {
    cout<<"Square: Circumference = "<<(4 * length)<<endl;
  }
  void Circumference(int length, int breadth)
  {
    Circumference(length);
  }
};

//Derived class - Inherits Shape as Private as Area and Circumference 
//for Square is very different from the Base class
class Circle : private Shape {
public:
  //Overloaded Area 
  void Area(int radius)
  {
    cout<<"Circle: Area = "<<(3.14 * radius * radius)<<endl;
  }
  //Overloaded Circumference 
  void Circumference(int radius)
  {
    cout<<"Circle: Circumference = "<<(2 * 3.14 * radius)<<endl;
  }
private:
  //Nobody should call these methods
  void Area(int length, int breadth) {}; 
  void Circumference(int length, int breadth) {}; 
};

int main()
{
  Rectangle r;
  cout<<"\n\nRectangle Class - Dimensions 3 x 4"<<endl;
  r.Area(3, 4);
  r.Circumference(3, 4);

  Square s;
  cout<<"\n\nSquare Class - Dimensions 3 x 3"<<endl;
  s.Area(3);
  Shape *s1 = &s; //possible to access derived class through base
  s1->Area(3,3);
  s.Circumference(3);

  Circle c;
  cout<<"\n\nCircle Class - Radius is 3"<<endl;
  //c.Area(3,3); //- Not Possible as its private in Circle
  c.Area(3);
  //Shape *c1 = &c; // not possible because conversion from 'Circle *' 
                    // to 'Shape *' exists, but is inaccessible
  //c.Circumference(3,3); //- Not Possible as its private in Circle
  c.Circumference(3);
  return 0;
}

The output of the program is as follows:

Program to print itself

I came across this interesting program that can print itself. I have modified it from C to C++ and added few comments. Its worth exploring.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//Challenge program to self print itself
//Original from http://www.cprogramming.com/challenges/solutions/self_print.html
#include<iostream>
char *program = "#include <iostream>%cchar *program = %c%s%c;%cint main()%c{%c  printf(program, 10, 34, program, 34, 10, 10, 10, 10, 10, 10);%c  return 0;%c}%c";
int main()
{
  printf(program, 10, 34, program, 34, 10, 10, 10, 10, 10, 10);
  return 0;
}
//Note the trick
//In ASCII, 10 = LF or new line feed
//In ASCII, 34 = double quotes or "
//%c is printing charachter. 10 for new line and 34 for double quotes
//%s is printing the string

The output is as follows. Note that the aim is for the program to print itself and not the comments. Also the output is wrapped around.

Simulating FIFO behaviour with priority queues for equal priorities

In priority queue, the C++ specifications does not define the behaviour of the algorithms when equal-priority items are involved. It is assumed that the ordering is not important in case of a priority queue as long as the same priority items are in correct order as compared to other priorities. For a programmer though this can be important as he expects FIFO ordering for same priority items. To overcome the problem I mentioned in earlier program, we can add another item to get correct FIFO ordering for same priority items.

This is just one approach and there may be other approaches. Also notice that I have used a local variable which requires the order to be input. You can also use the static variable approach for this.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//Example of slightly advanced priority queue making sure that
//along with priorities, queue functionality of FIFO is maintained
#include <iostream>
#include <string>
#include <vector>
#include <queue>

using namespace std;

class PrioritizedWord
{
private:
  int m_prio;
  string m_word;
  int m_order; //To set FIFO operation

public:
  explicit PrioritizedWord()
  { }
  explicit PrioritizedWord(const std::string& word, const int priority = 0, const int order = 0): 
                                   m_word(word), m_prio(priority), m_order(order)
  { }
  //Operator overloading for priority comparison
  const bool operator <(const PrioritizedWord& pW) const
  {
    if(m_prio == pW.m_prio)
      return (m_order > pW.m_order);
    else
      return (m_prio < pW.m_prio);
  }
  //Operator overloading to print output 
  friend ostream& operator <<(ostream& out, const PrioritizedWord& pW)
  {
    out<<pW.m_word;
    return out;
  }
  int getPrio(void)
  {return m_prio;}
  string getWord(void)
  {return m_word;}
};

int main()
{
  priority_queue<PrioritizedWord> zahidQueue;

  //Note the final order will not be the same as the specs do not
  //define behaviour in case two numbers with equal priority exist
  zahidQueue.push(PrioritizedWord("First", 23, 1));
  zahidQueue.push(PrioritizedWord("Second", 23, 2));
  zahidQueue.push(PrioritizedWord("Third", 23, 3));
  zahidQueue.push(PrioritizedWord("Fourth", 51, 4));
  zahidQueue.push(PrioritizedWord("Fifth", -1, 5));

  cout<<"\n\nZahid Queue elements :"<<endl;
  while(!zahidQueue.empty())
  {
    cout<<zahidQueue.top()<<" "<<endl;
    zahidQueue.pop();
  }

  return 0;
}

The output is as follows:

Basic String manipulation example

The following is a basic string manipulation example

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program intends to show basic string operations
#include<iostream>
#include<string>

using namespace std;

int main(void)
{
  //Lets ask for a name and make a banner to welcome the person
  //Adapted from Accelerated C++ by Andrew Koenig and Barbara Moo 
  string name;
  cout << "\nHello, what is your name? ";
  cin >> name;
  cout << "\n\n\n\n";
  string banner = "Welcome " + name; //String addition
  int bannerSize = banner.size(); //We use this size for everything
  string stars((bannerSize + 4), '*');
  string filler(bannerSize, ' ');
  cout << stars << endl;
  cout << "* " << filler << " *" << endl;
  cout << "* " << banner << " *" << endl;
  cout << "* " << filler << " *" << endl;
  cout << stars << endl;

  //Now lets check some basic string pointer operations
  cout<<"\n\n\n\n";
  string strs;
  {
    char *text="Some program";
    cout<<"text = "<<text<<endl;

    //copying char* to string
    strs = text;
    //text[0]='A'; //-- Not possible. Run time crash as text is const pointer
    cout<<"str locally = "<<strs<<endl;
  }
  cout<<"str globally = "<<strs<<endl;

  return 0;
}

The output is as follows:

Example of friend class and friend function

The following example shows a simple friend class and friend function example:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program shows a basic example of friend class and function
#include<iostream>

using namespace std;

class A {
public:
  int square(int num)
  {return num*num;}
protected:
  int reduced_square(int num)
  {return (num-1)*(num-1);}
private:
  int cube(int num)
  {return num*num*num;}
  friend class B;
};

//Class B friend of class A
class B {
public:
  int b_square(int num)
  {
    A a;
    return a.square(num);
  }
  int b_reduced_square(int num)
  {
    A a;
    return a.reduced_square(num);
  }
  int b_cube(int num)
  {
    A a;
    return a.cube(num);
  }
private:
  int b_priv;
  int b_default_cube()
  { 
    return b_cube(b_priv); 
  }
  friend int C(int c);
};

//function C friend of Class B
int C(int c)
{
  B b;
  b.b_priv = c;
  //A a;
  //return a.cube(b.b_priv); - Not possible as C is not friend of A
  return b.b_default_cube();
}


int main()
{
  cout<<"\nExample of Friend Class and Function"<<endl;
  A a;
  cout<<"\nA: Square of 3 = "<<a.square(3)<<endl;
  //The following is not possible
  //cout<<"Reduced Square of 3 = "<<a.reduced_square(3)<<endl;
  //cout<<"Cube of 3 = "<<a.cube(3)<<endl;

  B b;
  cout<<"\nB: Square of 4 = "<<b.b_square(4)<<endl;
  cout<<"B: Reduced Square of 4 = "<<b.b_reduced_square(4)<<endl;
  cout<<"B: Cube of 4 = "<<b.b_cube(4)<<endl;

  cout<<"\nC: Cube of 5 = "<<C(5)<<endl;

  return 0;
}

The output is as follows:

An example of bound C++ maps

The following example shows how to define a bound C++ map which can only contain maximum number of specified elements. This is just an approach and there will probably be better and more efficient approaches.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//The example below shows a bound map. In a general C++ map you
//can add as many elements as required. In this case there can
//only be 10 elements in the map. If you try adding more it will
//generate an error
#include<iostream>
#include<map>
#include<string>
#include<assert.h>

using namespace std;

map<int, string> freq;
int a[10]={0,0,0,0,0,0,0,0,0,0};

int store_in_maps(string s)
{
  int i;
  for(i=0; i < 10; i++)
  {
    if (a[i]==0)
      break;
  }
  if(i==10)
  {
    cout<<"Sorry no more Ids available in the pool"<<endl;
    assert(0);
  }

  a[i]=1;
  freq[i] = s;
  return i;
}

int remove_from_map(string s)
{
  map<int, string>::const_iterator iter;
  for(iter=freq.begin(); iter != freq.end(); ++iter)
  {
    if(iter->second == s)
      break;
  }
  if(iter==freq.end())
  {
    cout<<"Cant find the string "<<s<<endl;
    return (-1);
  }
  a[iter->first]=0;
  return iter->first;
}


int main()
{
  store_in_maps("first");
  store_in_maps("second");
  store_in_maps("third");
  store_in_maps("fourth");
  store_in_maps("fifth");
  store_in_maps("sixth");
  store_in_maps("seventh");
  store_in_maps("eighth");
  store_in_maps("ninth");
  store_in_maps("tenth");
  remove_from_map("fifth");
  store_in_maps("eleventh");
  remove_from_map("zahid");
  remove_from_map("fourth");

  map<int, string>::const_iterator iter;
  for(iter=freq.begin(); iter != freq.end(); ++iter)
  {
    cout<<"First: "<<(iter->first)<<"     Second: "<<(iter->second)<<"\t\tPool value: "<<a[iter->first]<<endl;
  }

  return 0;
}

The output of the program is as follows:

An example of advanced erase in C++ maps

The following example shows how to use erase in C++ maps

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program shows an example of how C++ maps erase work.
#include <iostream>
#include <map>

using namespace std;

int main ()
{
  map<char,int> zgmap;
  map<char,int>::iterator it,it_low,it_up;

  zgmap['a']=1;
  zgmap['b']=2;
  zgmap['c']=3;
  zgmap['d']=4;
  zgmap['e']=5;
  zgmap['g']=6;
  zgmap['j']=7;
  zgmap['n']=8;

  it_low=zgmap.lower_bound ('c');  // it_low points to c
  it_up=zgmap.upper_bound ('j');   // it_up points to n and not j

  zgmap.erase(it_low,it_up);        // erases all elements from c to j

  //Print Map contents
  cout<<"\n** Printing the zgmap contents **"<<endl;
  for ( it=zgmap.begin() ; it != zgmap.end(); it++ )
  {
    cout << (*it).first << " => " << (*it).second << endl;
  }

  return 0;
}

The output of the program is as follows:

An example of C++ maps

The following example shows the working of C++ maps. This also has a simple example of union which is sometimes used in C and C++ programs

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program shows an example of how maps work.
//In maps, the first parameter is key and second value
//The keys in the map are automatically softed from lower to higher
#include<iostream>
#include<map>
#include<string>

using namespace std;

//defining a union that is used with newMap_
union uu
{
  char c;
  int i;
} u;

//Lets define two different maps
//The first parameter is key and second value
map<string, int> portMap_;
map<void *, uu> newMap_;

int main()
{
  //first entry in portmap
  portMap_["first"] = 1;

  //example of using the iterator
  map<string, int>::const_iterator it;
  string z = "second";
  it = portMap_.find(z); //not in the map so wont be found
  if(it == portMap_.end())
  {
    portMap_[z] = 22; //add second element
  }

  //Add thrid element directly
  z = "third";
  portMap_[z] = 12345;

  //Add 4th element by insert
  portMap_.insert(pair<string,int>("fourth", 4444)); 

  //Add 5th element by insert
  portMap_.insert(pair<string,int>("fifth", 5555)); 


  cout<<"\n** Printing the portmap_ values **"<<endl;
  for(it = portMap_.begin(); it != portMap_.end(); ++it)
    cout<<"Key = "<<it->first<<"   Val = "<<it->second<<endl;

  cout<<"\n** Removing fourth element **"<<endl;
  z = "fourth";
  it = portMap_.find(z);
  portMap_.erase(it);

  cout<<"\n** Printing the portmap_ values **"<<endl;
  for(it = portMap_.begin(); it != portMap_.end(); ++it)
    cout<<"Key = "<<it->first<<"   Val = "<<it->second<<endl;

  //Playing with New Map
  cout<<"\n\nCreating New Map whose key is a void pointer"<<endl;

  uu u_val1, u_val2;
  void *val1, *val2;
  u_val1.i = 70, val1 = &u_val1;
  newMap_[val1]=u_val1;

  val2 = val1;
  map<void *, uu>::const_iterator it_new;
  it_new = newMap_.find(val2);
  if(it_new != newMap_.end())
  {
    u_val2 = it_new->second;
    cout<<"Note that since u_val2 is a union you can print i or c as required"<<endl;
    cout<<"val2 = "<<val2<<"    value.c = "<<u_val2.c<<endl;
    cout<<"val2 = "<<val2<<"    value.i = "<<u_val2.i<<endl;
  }

  return 0;
}

The output is as follows:

Multi-threading with Thread Synchronisation

Here is an example explaining the concept of multiple threads and their synchronisation:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//Example from http://www.adrianxw.dk/SoftwareSite/Threads/Threads2.html
//This shows an example of Multithreading and thread synchronisation
#include <windows.h>
#include <process.h>
#include <iostream>
using namespace std;

void Func1(void *);
void Func2(void *);

CRITICAL_SECTION Section; //This will act as Mutex


int main()
{
  HANDLE hThreads[2];
  InitializeCriticalSection(&Section);

  //Create two threads and start them
  hThreads[0] = (HANDLE)_beginthread(Func1, 0, NULL);
  hThreads[1] = (HANDLE)_beginthread(Func2, 0, NULL);

  //Makes sure that both the threads have finished before going further
  WaitForMultipleObjects(2, hThreads, TRUE, INFINITE);

  //This is done after all threads have finished processing
  DeleteCriticalSection(&Section);

  cout << "Main exit" << endl;
  return 0;
}

void Func1(void *P)
{
  int Count;

  for (Count = 1; Count < 11; Count++)
  {
    EnterCriticalSection(&Section);
      cout << "Func1 loop " << Count << endl;
    LeaveCriticalSection(&Section);
  }
  return;
}

void Func2(void *P)
{
  int Count;

  for (Count = 10; Count > 0; Count--)
  {
    EnterCriticalSection(&Section);
      cout << "Func2 loop " << Count << endl;
    LeaveCriticalSection(&Section);
  }
  return;
}

The output is as follows:
Complete explanation of the above program is available here.

Simple example of Priority Queue

Here is a simple example of priority queue:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy

//Example showing how simple priority queues work using C++

#include <iostream>

#include <string>

#include <vector>

#include <queue>



using namespace std;



class PrioritizedWord

{

private:

  int m_prio;

  string m_word;



public:

  explicit PrioritizedWord()

  { }

  explicit PrioritizedWord(const std::string& word, const int priority = 0):

                                   m_word(word), m_prio(priority)

  { }

  //Operator overloading for priority comparison

  const bool operator <(const PrioritizedWord& pW) const

  {

    return (m_prio < pW.m_prio);

  }

  //Operator overloading to print output

  friend ostream& operator <<(ostream& out, const PrioritizedWord& pW)

  {

    out<<pW.m_word;

    return out;

  }

  int getPrio(void)

  {return m_prio;}

  string getWord(void)

  {return m_word;}

};



int main()

{

  int somenum = 2;

  while(somenum > 0)

  {

    priority_queue<PrioritizedWord> wordQueue, zahidQueue, *temp=NULL;

    //Word Queue first time, Zahid Queue second time

    if(somenum%2==0)

    {

      temp = &wordQueue;

    }

    else

    {

      temp = &zahidQueue;

    }



    //Note the final order will not be the same as the specs do not

    //define behaviour in case two numbers with equal priority exist

    temp->push(PrioritizedWord("First", 23));

    temp->push(PrioritizedWord("Second", 23));

    temp->push(PrioritizedWord("Third", 23));

    temp->push(PrioritizedWord("Fourth", 51));

    temp->push(PrioritizedWord("Fifth", -1));



    cout<<"\n\nWord Queue elements (All elements lost):"<<endl;

    while(!wordQueue.empty())

    {

      cout<<wordQueue.top()<<" "<<endl;

      wordQueue.pop();

    }



    cout<<"\n\nZahid Queue elements (Elements preserved):"<<endl;

    if(!zahidQueue.empty())

    {

      priority_queue<PrioritizedWord>    tempQueue;

      while(!zahidQueue.empty())

      {

        PrioritizedWord &temppW = zahidQueue.top();

        cout<<temppW<<" "<<endl;

        tempQueue.push(PrioritizedWord(temppW.getWord(), temppW.getPrio()));

        zahidQueue.pop();

      }

      while(!tempQueue.empty())

      {

        PrioritizedWord &temppW = tempQueue.top();

        zahidQueue.push(PrioritizedWord(temppW.getWord(), temppW.getPrio()));

        tempQueue.pop();

      }

    }



    cout<<"\n\nZahid Queue - Removing an element and leaving the rest"<<endl;

    {

      priority_queue<PrioritizedWord>    tempQueue;

      while(!zahidQueue.empty())

      {

        PrioritizedWord &temppW = zahidQueue.top();



        if(temppW.getWord() != "Second")

        {

          tempQueue.push(PrioritizedWord(temppW.getWord(), temppW.getPrio()));

          zahidQueue.pop();

        }

        else

        {

          zahidQueue.pop();

          break;

        }

      }

      while(!tempQueue.empty())

      {

        PrioritizedWord &temppW = tempQueue.top();

        zahidQueue.push(PrioritizedWord(temppW.getWord(), temppW.getPrio()));

        tempQueue.pop();

      }

    }



    cout<<"\n\nZahid Queue elements after removal of element"<<endl;

    while(!zahidQueue.empty())

    {

      cout<<zahidQueue.top()<<" "<<endl;

      zahidQueue.pop();

    }

    somenum--;

  }



  return 0;

}

The output is as follows:

More on Vector Manipulation

This is slightly advanced vector manipulation program

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//This program shows advanced vector manipulation
#include<iostream>
#include<vector>

using namespace std;

//This method prints the vector
void printer(vector<int> v)
{
  unsigned int i;
  cout << "Size = " << v.size() << endl;
  cout << "Contents = ";
  for(i = 0; i <v.size(); i++)
     cout<<v[i]<<"   ";
  cout<<endl;
}

//Overloaded method same as above but takes pointers
void printer(vector<int*> v)
{
  unsigned int i;
  cout << "\nOverloaded Method " << endl;
  cout << "Size = " << v.size() << endl;
  cout << "Contents = ";
  for(i = 0; i <v.size(); i++)
     cout<<*v[i]<<"   ";
  cout<<endl;
}

int main()
{
  vector<int> v1(5, 1);
  cout<<"** Original **"<<endl;
  printer(v1);

  unsigned int i;
  //Modifying the list above
  for(i = 0; i < v1.size(); i++)
    v1[i] = i + 3;
  cout<<"\n** Modified **"<<endl;
  printer(v1);

  vector<int>::iterator it;
  //Inserting in the list after the first element '0' and after the 4th elem '9 9 9 9'
  it = v1.begin();
  it += 1;
  v1.insert(it,0);
  it = v1.begin(); //Crash if you dont do this
  it += 5; //Because we inserted '0', 4th element has become 5th.
  v1.insert(it, 4, 9);
  cout<<"\n** After Insert **"<<endl;
  printer(v1);

  //Testing Pop back - removes element from the end
  v1.pop_back();
  v1.pop_back();
  cout<<"\n** After couple of Pop back's **"<<endl;
  printer(v1);

  //New Vector
  cout<<endl<<"\n**********  NEW  *************"<<endl;
  vector<int*> v2;
  int *a=new int(5);
  int *b=new int(6);
  int *c=new int(7);
  int *d=new int(11);
  v2.push_back(a);
  v2.push_back(b);
  v2.push_back(c);
  printer(v2);
  cout<<"\ntwo pop_back and a push_back"<<endl;
  v2.pop_back();
  v2.pop_back();
  v2.push_back(d);
  printer(v2);
  cout<<"\nClear Vector two"<<endl;
  v2.clear();
  printer(v2);

  return 0;
}

The output is as follows:

Basic Vector Manipulation

Here is an example of basic vector manipulation

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy

//This program shows how to create vectors, check size and capacity,

//change the value of the elements and finally clear the vector

#include <iostream>

#include <vector>



using namespace std;



int main()

{

  //Create a vector called vectorOne

  vector<int> vectorOne; //Note size is 0

  //Resize to 3 with default value 7

  vectorOne.resize(3,7);

  //Print the output to see the resize

  cout<<"Test 1"<<endl;

  for(unsigned i=0;i<vectorOne.size();i++)

  {

    cout<<"Element: "<<i<<"     Value: "<<vectorOne.at(i)<<endl;

  }



  //Resize further to 7 and new values default to 4

  vectorOne.resize(7,4);

  cout<<"\nTest 2"<<endl;

  for(unsigned i=0; i<vectorOne.size(); i++)

  {

    cout<<"Element: "<<i<<"     Value: "<<vectorOne.at(i)<<endl;

  }



  //Check what the size and capacity of the vector is

  cout<<endl;

  cout<<"Size of vectorOne is: "<<vectorOne.size()<<endl;

  cout<<"Capacity of vectorOne is: "<<vectorOne.capacity()<<endl;



  //Lets modify the values of these vectors

  for(unsigned i=0,j=22;i<vectorOne.size();i++,j+=i)

  {

    vectorOne.at(i)=j;

  }



  cout<<"\nTest 3"<<endl;

  for(unsigned i=0; i<vectorOne.size(); i++)

  {

    cout<<"Element: "<<i<<"     Value: "<<vectorOne.at(i)<<endl;

  }



  //Use reserve to reallocate vectorOne with enough storage for 10 elements

  vectorOne.reserve(10);

  cout<<"\nSize of vectorOne is: "<<vectorOne.size()<<endl;

  cout<<"Capacity of vectorOne is: "<<vectorOne.capacity()<<endl;



  //Try resizing to 15 and dont add any default values for the new elements

  vectorOne.resize(15);

  cout<<"\nSize of vectorOne is: "<<vectorOne.size()<<endl;

  cout<<"Capacity of vectorOne is: "<<vectorOne.capacity()<<endl;



  //Remove all elements of the vector

  vectorOne.clear();

  cout<<"\nVector Cleared"<<endl;

  cout<<"Size of vectorOne is: "<<vectorOne.size()<<endl;

  cout<<"Capacity of vectorOne is: "<<vectorOne.capacity()<<endl;

  cout<<endl;



  return 0;

}

The output of the program is as follows: