View Compilation Error

0_0_30167172_15386.cpp: In function 'int main()':
0_0_30167172_15386.cpp:12:24: error: 'angle' was not declared in this scope
     double s1=pi/n-sin(angle)/2;
                        ^
0_0_30167172_15386.cpp:14:5: error: 'res' was not declared in this scope
     res-=(n-1)*s1;
     ^