foo.cpp: In function 'void add_edge(int, int, int, int)':
foo.cpp:24:40: warning: narrowing conversion of 'G[to].std::vector<_Tp, _Alloc>::size<edge, std::allocator<edge> >()' from 'std::vector<edge>::size_type {aka unsigned int}' to 'int' inside { } is ill-formed in C++11 [-Wnarrowing]
  edge e1 = { to, cap, cost, G[to].size() };
                                        ^
foo.cpp:25:43: warning: narrowing conversion of 'G[from].std::vector<_Tp, _Alloc>::size<edge, std::allocator<edge> >()' from 'std::vector<edge>::size_type {aka unsigned int}' to 'int' inside { } is ill-formed in C++11 [-Wnarrowing]
  edge e2 = { from, 0, -cost, G[from].size() };
                                           ^
foo.cpp: In function 'bool spfa(int)':
foo.cpp:44:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < G[t].size(); i++)
                                 ^
foo.cpp: At global scope:
foo.cpp:82:22: error: '_TCHAR' has not been declared
 int _tmain(int argc, _TCHAR* argv[])
                      ^