for...to...do:

uses crt;
var s,i:integer;
begin
   clrscr;
   for i:=1 to 100 do s:=s+i;
   write('Tong la: ',s);
   readln
end.

while...do:

uses crt;
var s,i:integer;
begin
   clrscr;
   while i<=100 do 
   begin
      i:=i+1;
      s:=s+i;
   end;
   write('Tong la: ',s);
   readln
end.

While do

---

Program HuynhDucNhatDeThuongQuaDiA;
Uses crt;
Var HDNCute,i: longint;
Begin
        Clrscr;
        HDNCute:=0; i:=1;
        While i<=100 do
        Begin
                HDNCute:=HDNCute+i;
                inc(i);
        End;

        Write('S = ',HDNCute);
        Readln
End.

---

For do

---

Program HuynhDucNhatDeThuongQuaDiA;
Uses crt;
Var HDNCute,i: longint;
Begin
        Clrscr;
        For i:=1 to 100 do
                HDNCute:=HDNCute+i;

        Write('S = ',HDNCute);
        Readln
End.

---

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