View Compilation Error

0_0_28494205_19362.cpp: In function 'void build(int, double)':
0_0_28494205_19362.cpp:18:22: error: 'M_PI' was not declared in this scope
         if((i-1)*jd<=M_PI/2)
                      ^
0_0_28494205_19362.cpp: In function 'int main()':
0_0_28494205_19362.cpp:97:37: error: 'M_PI' was not declared in this scope
             double jd=(double)z/180*M_PI;
                                     ^