View Compilation Error

0_0_30124098_568.cpp: In function 'int find(int)':
0_0_30124098_568.cpp:32:11: error: 'pre' was not declared in this scope
     while(pre[r]!=r)    r=pre[r];//查找到根节点为止   
           ^
0_0_30124098_568.cpp:35:11: error: 'pre' was not declared in this scope
         j=pre[i];  
           ^