View Compilation Error

0_0_29596088_8444.cpp: In function 'void cdq(int, int)':
0_0_29596088_8444.cpp:45:32: error: 'mid' was not declared in this scope
   if((a[j].y<=a[k].y||k>r)&&j<=mid)
                                ^
0_0_29596088_8444.cpp:51:9: error: 'struct node' has no member named 'a'
    b[i].a[k++];
         ^
0_0_29596088_8444.cpp:57:9: error: 'mid' was not declared in this scope
   if(i<=mid)insert(a[i].z,-1);
         ^