foo.cc: In function 'void dijkstra(int, int)':
foo.cc:45:20: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
             if(u==a&&e.to==b||u==b&&e.to==a)continue;//是个无向图 
                ~~~~^~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:58:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&n,&m);
     ~~~~~^~~~~~~~~~~~~~
foo.cc:59:31: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for(int i=1;i<=n;i++)scanf("%d%d",&x[i],&y[i]);
                          ~~~~~^~~~~~~~~~~~~~~~~~~~
foo.cc:61:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d",&from,&to);
         ~~~~~^~~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。