View Compilation Error

0_0_20041953_23691.cpp: In function 'void FFT(cop*, int, int)':
0_0_20041953_23691.cpp:40:19: error: 'M_PI' was not declared in this scope
   cop step={cos(2*M_PI*type/h),sin(2*M_PI*type/h)};
                   ^