/in/foo.cc: In function 'int main()':
/in/foo.cc:13:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<=n;i++)
              ~^~~
/in/foo.cc:22:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<=n;i++)
              ~^~~
/in/foo.cc:25:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(a[i]-a[head]<=c3)
      ~~~~~~~~~~~~^~~~
/in/foo.cc:29:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     while(a[i]-a[head]>c3)
           ~~~~~~~~~~~~^~~