View Compilation Error

0_0_32634069_11609.cpp:10:14: error: array bound is not an integer constant before ']' token
 double v[MAXN];
              ^
0_0_32634069_11609.cpp: In function 'int ff(double)':
0_0_32634069_11609.cpp:19:20: error: 'v' was not declared in this scope
         double Vy0=v[i]*sin(x);
                    ^
0_0_32634069_11609.cpp: In function 'int main()':
0_0_32634069_11609.cpp:35:24: error: 'v' was not declared in this scope
           scanf("%lf",&v[i]);
                        ^