0_0_30406326_27089.cpp: In function 'int main()': 0_0_30406326_27089.cpp:10:13: error: 'M_PI' was not declared in this scope #define pai M_PI ^ 0_0_30406326_27089.cpp:14:17: note: in expansion of macro 'pai' double alpha=2*pai/(double)n; ^