Tham khảo:
* Lặp tiến :
uses crt;
var i, n, P : longint;
begin
clrscr;
P := 1;
write('nhap so n : '); readln(n);
for i := 1 to n do P := P * i;
writeln(n,'! = ', P);
readln
end.
* Lặp lùi :
uses crt;
var i, n, P : longint;
begin
clrscr;
P := 1;
write('nhap so n : '); readln(n);
for i := n downto 1 do P := P * i;
writeln(n,'! = ', P);
readln
end.