Example 1 : 

#include <iostream>
using namespace std;

int main() {
  int a;

  cout << "Input a number. \n";
  cin >> a;
  if (a > 2*(a/2)) 
    cout << "That's odd ! \n";
  else 
    cout << "That's even. \n";

  return 0;
}


Example 2 : 

#include <iostream>
using namespace std;

int main() {
  int a;

  cout << "What's your age ? \n";
  cin >> a;
  if (a >= 70) 
    cout << "You are a P.G.O.M.L.D.A.D.L.D. \n";
  else if (a >= 65) 
    cout << "You are a P.G.O.M.L.D.A.D. \n";
  else if (a >= 60) 
    cout << "You are a P.G.O.M.L.D. \n";
  else 
    cout << "You are not old yet. \n";

  return 0;
}

Example 3 : calculates the length of a body travelling at 
a velocity v given its length when it is at rest.

#include <iostream>
#include <cmath>
#define c 300
using namespace std;

int main() {
  float restlen, vel, rellen;

  cout << "Input rest length(in m) and velocity(in 1000 km/s).\n";
  cin >> restlen >> vel;
  if (vel > 300) {
    cout << "Impossible. A body cannot travel faster than light !\n";
  } else {
    rellen = restlen*sqrt(1 - vel*vel/(c*c));
    cout << "Length = " << rellen << " meters.\n";
  } 

  return 0;
}