View Compilation Error

0_0_33541300_16467.cpp: In function 'int main()':
0_0_33541300_16467.cpp:237:61: error: 'M_PI' was not declared in this scope
             double used_area = center_area + center_p * R + M_PI * R * R;
                                                             ^
0_0_33541300_16467.cpp:243:12: error: expected ';' at end of input
     return 0
            ^
0_0_33541300_16467.cpp:243:12: error: expected '}' at end of input