View Compilation Error

0_0_20698904_17911.cpp:19:18: error: array bound is not an integer constant before ']' token
 vector<int> g[len];
                  ^
0_0_20698904_17911.cpp:106:13: error: array bound is not an integer constant before ']' token
 bool vis[len];
             ^
0_0_20698904_17911.cpp: In function 'bool dfs(int, int)':
0_0_20698904_17911.cpp:111:19: error: 'g' was not declared in this scope
     for(int i=0;i<g[a].size();i++)
                   ^
0_0_20698904_17911.cpp:113:12: error: 'vis' was not declared in this scope
         if(vis[g[a][i]]==1) continue;
            ^
0_0_20698904_17911.cpp:114:9: error: 'vis' was not declared in this scope
         vis[g[a][i]]=1;
         ^
0_0_20698904_17911.cpp: In function 'int main()':
0_0_20698904_17911.cpp:135:13: error: 'g' was not declared in this scope
             g[i].clear();
             ^
0_0_20698904_17911.cpp:147:17: error: 'g' was not declared in this scope
                 g[a].push_back(b);
                 ^
0_0_20698904_17911.cpp:168:22: error: 'vis' was not declared in this scope
                 fill(vis,vis+len,0);
                      ^