/in/foo.c: In function 'main':
/in/foo.c:11:27: warning: array subscript has type 'char' [-Wchar-subscripts]
  for(int i=0;i<ls;i++) vis[s[i]]++;
                           ^
/in/foo.c:12:27: warning: array subscript has type 'char' [-Wchar-subscripts]
  for(int i=0;i<lt;i++) vis[t[i]]=0;
                           ^
/in/foo.c:13:30: warning: array subscript has type 'char' [-Wchar-subscripts]
  for(int i=0;i<ls;i++) if(vis[s[i]]) putchar(s[i]);
                              ^