Add some oo exercise

code/modern_oo/solution/particles.sol.cpp

+#include <cstdlib> // pour std::rand()
+#include <iostream>
+#include <string>
+
+class Particle
+ {
+  public  :
+    Particle( double mass ) : mass_(mass) {}
+    Particle( const Particle & ) = delete ;
+    virtual ~Particle() = default ;
+    double mass() { return mass_ ; }
+    virtual std::string name() { return "Particle" ; }
+  private  :
+    double mass_ ;
+ } ;
+
+class ChargedParticle : public Particle
+ {
+  public  :
+    ChargedParticle( double mass, double charge )
+     : Particle(mass), charge_(charge) {}
+    double charge() { return charge_ ; }
+    std::string name() override { return "ChargedParticle" ; }
+  private  :
+    double charge_ = 0.0 ;
+ } ;
+
+void display( Particle & p  )
+ {
+  std::cout << p.name() << std::endl ;          
+  std::cout << "  mass = " << p.mass() << std::endl ;         
+ }
+
+int main()
+ {
+  for ( int i = 0 ; i < 5 ; ++i )
+   {
+    if ( std::rand() < (0.5 *  double(RAND_MAX)) )
+     {
+      Particle p(2) ;
+      display(p) ;
+     }
+    else
+     {
+      ChargedParticle p(1,1) ;
+      display(p) ;
+      std::cout << "  charge = " << p.charge() << std::endl ;         
+     }
+   }
+ }
\ No newline at end of file