View Compilation Error

0_0_20474866_7583.cpp: In function 'void quicksort(int*, int, int)':
0_0_20474866_7583.cpp:10:31: error: 'mid' was not declared in this scope
         while(l < r && a[l] < mid) l++;
                               ^
0_0_20474866_7583.cpp:11:31: error: 'mid' was not declared in this scope
         while(l < r && a[r] > mid) r--;
                               ^