Cách 1: For to do:

Program trafficjams;

Uses crt;

Var i,n,S:integer;

Begin

clrscr;

write('nhap gia tri cho n:');readln(n);

for i:=1 to n do S:=S+i;

write('tong la',S);

readln;

end.

Cách 2: While do:

Program trafficjamss;

Uses crt;

Var i,n,S:integer;

Begin

clrscr;

write('nhap gia tri cho n:');readln(n);

i:=1;

while i<=n do 

Begin

S:=S+i; i:=i+1;

end;

write('tong la',S);

readln;

end.

- For ... to .. do :

uses crt;

var k, n, X : integer;

begin

clrscr;

write('Nhap so n = '); readln(n);

X := 0;

for k := 1 to n do X := X + k;

write('Tong tu 1 - n = ', X);

readln

end.

- While .. do :

uses crt;

var k, n, X : integer;

begin

clrscr;

write('Nhap so n = '); readln(n);

X := 0; k := 1;

while k <= n do

    begin

        X := X + k;

        k := k + 1;

    end;

write('Tong tu 1 - n = ', X);

readln

end.