View Compilation Error

0_0_37997028_1712.cpp: In function 'void dfs(int)':
0_0_37997028_1712.cpp:17:18: error: 'head' was not declared in this scope
     for (int i = head[u]; i;i=nex[i]) {
                  ^
0_0_37997028_1712.cpp:17:31: error: 'nex' was not declared in this scope
     for (int i = head[u]; i;i=nex[i]) {
                               ^
0_0_37997028_1712.cpp:18:17: error: 'to' was not declared in this scope
         int v = to[i];
                 ^
0_0_37997028_1712.cpp: In function 'void dfs(int, int)':
0_0_37997028_1712.cpp:32:18: error: 'head' was not declared in this scope
     for (int i = head[u]; i;i=nex[i]) 
                  ^
0_0_37997028_1712.cpp:32:31: error: 'nex' was not declared in this scope
     for (int i = head[u]; i;i=nex[i]) 
                               ^
0_0_37997028_1712.cpp:34:17: error: 'to' was not declared in this scope
         int v = to[i];
                 ^