/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-1;i++)
              ~^~~~~
/in/foo.cc:25:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(a[tail]-a[head]<=c3)
      ~~~~~~~~~~~~~~~^~~~
/in/foo.cc:30:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     while(a[tail]-a[head]>c3)
           ~~~~~~~~~~~~~~~^~~