View Compilation Error

0_0_30619276_3477.cpp: In function 'int find(int)':
0_0_30619276_3477.cpp:24:13: error: 'a' was not declared in this scope
      if(pre[a] != a)
             ^
0_0_30619276_3477.cpp:29:16: error: 'a' was not declared in this scope
     return pre[a];
                ^