program tinhtong;

uses crt;

var i,n: integer;

      s: longint;

begin clrscr;

write('nhap n'); readln(n);

s:=0;

for i:=1 to n do if i mod 2 = 1 then s:=s+i;

write('tong la', s);

readln

end.

Câu lệnh lặp while....do:

program demo;

uses crt;

var i,n: integer;

      s: longint;

begin clrscr;

write('nhap n'); readln(n);

s:=0; i:=1;

while i <= n do

begin

  if i mod 2 = 1 then

   i:=i+1;

   s:=s+i;

end;

write('tong la', s);

readln

end.

For ... do ....

uses crt;
 var n, s, i : longint ;
  begin
   clrscr;
    write('N=');
     readln(n);
    for i := 1 to n do
        if i mod 2=1 
            then s := s + i ;
         writeln('S le :',s);
        end.

While ... do ...

uses crt;
 var n, s, i : longint ;
  begin
   clrscr;
    write('N=');
     readln(n);
      i := 1 ;
    while i<= n do
     begin
        if i mod 2=1 
            then s := s + i ;
        i := i + 1 ;
     end;
         writeln('S le :',s);
        end.