1/

var f:text;
begin
   assign(f,'KQ.TXT'); rewrite(f);
   writeln(f,21); writeln(f,11);
   close(f);
end.

2/ 

uses crt;
var s:string; i:byte;
begin
   clrscr;
   write('Nhap xau: '); readln(s);
   for i:=length(s) downto 1 do write(s[i]);
   writeln;
   for i:=1 to length(s) do
   if (s[i]>='A') and (s[i]<='z') then write(s[i]);
   readln
end.

a)

- Ghi dữ liệu vào tệp 'KQ.TXT' hai số 21 và 11 :

⇒ Writeln(f, 11); Writeln(f, 22);

b)

uses crt;

var S : string; i : byte;

begin

clrscr;

write('Nhau xau ki tu : '); readln(S);

write('Xau theo chieu nguoc : ');

for i := length(S) downto 1 do write(S[i]);

writeln; write('Cac chu cai : ');

for i := 1 to length(S) do

    begin

        if S[i] in ['A' .. 'Z'] then write(S[i]);

        if S[i] in ['a' .. 'z'] then write(S[i]);

    end;

readln

end.