View Compilation Error

0_0_26243874_27400.cpp: In function 'int main()':
0_0_26243874_27400.cpp:16:19: error: 'N' was not declared in this scope
         for(i=0;i<N;i++)
                   ^
0_0_26243874_27400.cpp:18:17: error: 'N' was not declared in this scope
         int x=a[N/2].x,y=a[N/2].y;
                 ^
0_0_26243874_27400.cpp:21:34: error: 'y' was not declared in this scope
             if((a[i].x>x&&a[i].y>y)||(a[i].x<x&&a[i].y<y))
                                  ^