/in/foo.c: In function 'main':
/in/foo.c:5:2: error: unknown type name 'in'
  in i,j=1,sum=0;
  ^~
/in/foo.c:7:13: error: 'n' undeclared (first use in this function)
  for(i=1;i<=n;i++)
             ^
/in/foo.c:7:13: note: each undeclared identifier is reported only once for each function it appears in