uses crt; var i,j,dem:integer; t:boolean; s:string; begin clrscr; write('Nhap xau: ');readln(s); dem:=0; for i:=1 to length(s) do begin t:=false; for j:=1 to i-1 do if ((s[i])=(s[j])) then t:=true; if not(t) then inc (dem); end; write('Co ',dem,' ki tu khac nhau'); readln end.
