View Compilation Error

0_0_22944991_3956.cpp: In function 'void sub(int, int, int)':
0_0_22944991_3956.cpp:27:8: error: 'a' was not declared in this scope
     if(a>(t[num].l+t[num].r)/2)
        ^
0_0_22944991_3956.cpp: In function 'void add(int, int, int)':
0_0_22944991_3956.cpp:37:8: error: 'a' was not declared in this scope
     if(a>(t[num].l+t[num].r)/2)
        ^