View Compilation Error

0_0_37874488_3587.cpp: In function 'void add(int, int, int)':
0_0_37874488_3587.cpp:24:18: error: 'head' was not declared in this scope
     e[idx].nxt = head[a];
                  ^
0_0_37874488_3587.cpp: In function 'void dfs(int, int)':
0_0_37874488_3587.cpp:60:17: error: 'head' was not declared in this scope
     for(int i = head[u]; i; i = e[i].nxt){
                 ^
0_0_37874488_3587.cpp: In function 'int main()':
0_0_37874488_3587.cpp:71:12: error: 'head' was not declared in this scope
     memset(head,0,sizeof head);
            ^