Example 1 : The class "colony" models an insect colony.
	    The program decides which insect colony is
            larger ...

#include <iostream>
#include <cmath>
using namespace std;

class colony{
private :
  int initial;
  float r1;
  float r2;
public :
  colony() {initial=0; r1=0; r2=0;}
  colony(int init, float a, float b) {initial = init; r1=a; r2=b;}
  void set(int i, float a, float b) {initial = i; r1=a; r2=b;}
  void get_data();

  int get_size(int n);
};

void colony :: get_data() {
  cout << "What is the initial population ?\n";
  cin >> initial;
  cout << "Input the rates of growth \n";
  cin >> r1 >> r2;
}

int colony :: get_size(int n) {
  float size = initial;

  for(int a=0; a<n; a++){
    if (a%2)
      size = floor(size*(1+r2/100));
    else 
      size = floor(size*(1+r1/100));
  }

  return (int) size;
}

int main() {
  colony ants, termites;
  int n;

  cout << "Enter data for the ant population \n";
  ants.get_data();
  cout << "Enter data for the termite population \n";
  termites.get_data();
  cout << "How many time periods have elapsed ?\n";
  cin >> n;
  if (ants.get_size(n) > termites.get_size(n))
    cout << "More ants than termites \n";
  else
    cout << "More termites than ants \n";

  return 0;
}



Example 2 : Complex numbers ... Only complex addition
            has been implemented.

#include <iostream>
#include <cmath>
using namespace std;

class complex{
private :
  float x,y;
public:
  complex() {x=0;y=0;}
  complex(float a) {x=a;y=0;}
  complex(float a, float b) {x=a;y=b;}

  float real_part() { return x;}
  float imaginary_part() {return y;}
  void display();
  void set(float a) {x=a;y=0;}
  void set(float a, float b) {x=a;y=b;}
  void get();
};

void complex :: display(){
  cout <<"(" << x << ") + i(" << y << ")\n";
}

void complex :: get() {
  float x,y;
  cout << "Input real part \n";
  cin >> x;
  cout << "Input imaginary part \n";
  cin >> y;
  set(x,y);
}

complex sum(complex z1, complex z2) {
  complex s;
  float x,y;

  x = z1.real_part() + z2.real_part();
  y = z1.imaginary_part() + z2.imaginary_part();
  s.set(x,y);

  return s;
}


int main() {
  complex z1, z2, z3;
  
  cout << "Input the first complex number \n";
  z1.get(); 
  cout << "Input the second complex number \n";
  z2.get();
  z3 = sum(z1, z2);
  cout << "The sum is \n";
  z3.display();

  return 0;
}