View Compilation Error

0_0_14947977_1023.cpp: In function 'double jd(double, double, double, double, double, double)':
0_0_14947977_1023.cpp:13:56: error: 'pi' was not declared in this scope
     return acos((aa*aa - bb*bb + cc*cc) / (2 * aa*cc))/pi*180.0;
                                                        ^
0_0_14947977_1023.cpp: In function 'int main()':
0_0_14947977_1023.cpp:29:48: error: 'pi' was not declared in this scope
         double r = l / (2 * sin(jdjd / 2.0/180*pi));
                                                ^