/in/foo.cc: In function 'int main()':
/in/foo.cc:16:24: warning: array subscript is below array bounds [-Warray-bounds]
   a[n-1]=abs(a[n]-a[n-1]);
                   ~~~~~^
/in/foo.cc:16:8: warning: array subscript is below array bounds [-Warray-bounds]
   a[n-1]=abs(a[n]-a[n-1]);
   ~~~~~^