Bài 1:

program bai_giai1;
uses crt;
var s,st:string;
    i:integer;
begin
    clrscr;
    write('Nhap xau: ');  readln(S);
    st:='';
    for i:=length(s) downto 1 do st:=st+s[i];
    write(st);
    readln;
end.

Bài 2:

  *   Cách thường:

program bai_giai2;
uses crt;
var a,b,c,max:integer;
begin
    clrscr;
    write('Nhap a: ');  readln(a);
    write('Nhap b: ');  readln(b);
    write('Nhap c: ');  readln(c);
    max:=a;
    if b>max then max:=b;
    if c>max then maX:=c;
    write('So lon nhat la: ',max);
    readln;
end.

 *    Chương trình con

program bai_giai2;
uses crt;
var a,b,c:integer;
function max(a,b,c:integer):integer;
begin
    max:=a;
    if b>max then max:=b;
    if c>max then maX:=c;
end;
begin
    clrscr;
    write('Nhap a: ');  readln(a);
    write('Nhap b: ');  readln(b);
    write('Nhap c: ');  readln(c);
    write('So lon nhat la: ',max(a,b,c));
    readln;
end.

1.

uses crt;
var s:string; i:longint;
begin
clrscr;  
   write('Nhap xau: ');readln(s);
   for i:=length(s) downto 1 do write(s[i]);
readln
end.

2.

Cách thông thường:

uses crt;
var a,b,c,max:longint;
begin
clrscr;  
   write('Nhap a: ');readln(a);
   write('Nhap b: ');readln(b);
   write('Nhap c: ');readln(c);
   max:=a;
   if max<b then max:=b;
   if max<c then max:=c;
   writeln(max);
readln
end.

Cách dùng chương trình con:

uses crt;
var a,b,c:longint;
function max(a,b:longint):longint;
begin
   max:=a; 
   if a<b then max:=b; 
end;
begin
clrscr;  
   write('Nhap a: ');readln(a);
   write('Nhap b: ');readln(b);
   write('Nhap c: ');readln(c);
   writeln(max(a,max(b,c)));
readln
end.