View Compilation Error

0_0_23266324_18224.cpp: In function 'bool f(double)':
0_0_23266324_18224.cpp:10:15: error: 'M_PI' was not declared in this scope
         temp+=M_PI*(2*(h[i]-x)*(h[i]-x)*(h[i]-x)/h[i]/h[i]-h[i])*r[i]*r[i]/3;
               ^