View Compilation Error

0_0_29130082_20783.cpp: In function 'void update(int, int, int, int, int, int)':
0_0_29130082_20783.cpp:40:11: error: 'mid' was not declared in this scope
     if(x<=mid)update(2*k,l,(l+r)/2,x,y,a);
           ^
0_0_29130082_20783.cpp:41:11: error: 'mid' was not declared in this scope
     if(y>=mid+1)update(2*k+1,(l+r)/2+1,r,x,y,a);
           ^