View Compilation Error

0_0_16981598_6718.cpp:1:9: error: 'maxn' was not declared in this scope
 int ans[maxn];///maxn是边的最大数量
         ^
0_0_16981598_6718.cpp:2:10: error: 'maxn' was not declared in this scope
 bool vis[maxn];
          ^
0_0_16981598_6718.cpp: In function 'void dfs(int)':
0_0_16981598_6718.cpp:6:15: error: 'head' was not declared in this scope
     for(int i=head[now];i!=-1;i=tu[i].next)
               ^
0_0_16981598_6718.cpp:6:33: error: 'tu' was not declared in this scope
     for(int i=head[now];i!=-1;i=tu[i].next)
                                 ^
0_0_16981598_6718.cpp:7:9: error: 'vis' was not declared in this scope
     if(!vis[i])
         ^
0_0_16981598_6718.cpp:12:9: error: 'ans' was not declared in this scope
         ans[bj++]=i;///等于i是记录边，等于tu[i].to是记录点
         ^