View Compilation Error

0_0_25395204_25264.cpp:8:29: error: array bound is not an integer constant before ']' token
 struct edge{int to,next;}g[N];
                             ^
0_0_25395204_25264.cpp: In function 'void add(int, int)':
0_0_25395204_25264.cpp:22:2: error: 'g' was not declared in this scope
  g[num].to = v;
  ^
0_0_25395204_25264.cpp: In function 'void tarjan(int, int)':
0_0_25395204_25264.cpp:64:30: error: 'g' was not declared in this scope
  for(int i = head[u];i!=-1;i=g[i].next)
                              ^