View Compilation Error

0_0_20570037_31009.cpp: In member function 'db C::inta_c(const C&) const':
0_0_20570037_31009.cpp:305:33: error: 'M_PI' was not declared in this scope
   if (d < c.r - r + eps) return M_PI*r*r;
                                 ^
0_0_20570037_31009.cpp:306:33: error: 'M_PI' was not declared in this scope
   if (d < r - c.r + eps) return M_PI*c.r*c.r;
                                 ^
0_0_20570037_31009.cpp: In function 'db ang(db)':
0_0_20570037_31009.cpp:335:21: error: 'M_PI' was not declared in this scope
  if (t < -eps) t += M_PI;
                     ^
0_0_20570037_31009.cpp:336:10: error: 'M_PI' was not declared in this scope
  if (t > M_PI-eps) t -= M_PI;
          ^
0_0_20570037_31009.cpp:337:27: error: 'M_PI' was not declared in this scope
  return max(t, 0.0)*180.0/M_PI;
                           ^