#include <iostream.h>
#include <math.h>
 const double pi = 3.14159;
/* variable globale accessible de toutes les parties 
du programme, ne peut etre modifiee, 
car declaree constante*/
double phase(double f , double t)   {
  //  return 2 * M_PI * f * t;
 return 2 * pi * f * t;    }
 int main ()  {
  double f = 20, t = 8.7;
//  pi = 2*pi;
 cout << " pi = 2*pi : " <<  pi << endl;
cout << " phase = " << phase(f,t) << endl;
cout <<" utilisation de M_PI -----> " << 
  2*M_PI*f*t << endl;    }