View Compilation Error

0_0_30466728_13175.cpp: In function 'int main()':
0_0_30466728_13175.cpp:66:41: error: 'vis' was not declared in this scope
         for(int i = 1; i <= m; i ++) if(vis[i] = Union(es[i].u, es[i].v))
                                         ^