/in/foo.c: In function 'output':
/in/foo.c:16:8: error: 'o' undeclared (first use in this function)
  for(i=o;i<10;i++)
        ^
/in/foo.c:16:8: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:17:12: warning: format '%d' expects argument of type 'int', but argument 2 has type 'int *' [-Wformat=]
   printf("%d",&a[i]);
            ^