View Compilation Error

0_0_14920535_28610.cpp: In function 'void add()':
0_0_14920535_28610.cpp:74:25: error: 'O' was not declared in this scope
  Point x = out.back() - O;
                         ^
0_0_14920535_28610.cpp:79:20: error: 'r' was not declared in this scope
  double Tmp = fabs(r * r * delta / 2.0);
                    ^
0_0_14920535_28610.cpp: In function 'int main()':
0_0_14920535_28610.cpp:114:23: error: 'i' was not declared in this scope
    scanf("%lf%lf", &p[i].x, &p[i].y);
                       ^
0_0_14920535_28610.cpp:131:8: error: expected primary-expression before ')' token
    if ()
        ^