/in/foo.cc:20:27: error: ISO C++ forbids declaration of 'add_edge' with no type [-fpermissive]
 add_edge(int u,int v,int w)
                           ^
/in/foo.cc: In function 'int add_edge(int, int, int)':
/in/foo.cc:26:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^