a)for..do

uses crt;
var i,n,s:longint;
begin
clrscr;
write('nhap so n:');readln(n);
s:=0;i:=1;
while i<=n do
begin
 s:=s+i;
 i:=i+1;
end;
write('tong cua n so tu nhien dau tien la:',s);
readln;
end.

b) for..fdo:

uses crt;
var i,n:longint;
s:real;
begin
clrscr;
write('nhap so n:');readln(n);
s:=0;
for i:=1 to n do s:=s+1/i;
write('tong cua n so tu nhien dau tien la:',s:4:2);
readln;
end.

while..do:

uses crt;
var i,n:longint;
s:real;
begin
clrscr;
write('nhap so n:');readln(n);
s:=0;i:=1;
while i<=n do
begin
 s:=s+1/i;
 i:=i+1;
end;
write('tong cua n so tu nhien dau tien la:',s:4:2);
readln;
end.

c) for..do:

uses crt;
var i,n:longint;
s:real;
begin
clrscr;
write('nhap so n:');readln(n);
s:=1;
for i:=1 to n do s:=s*i;
write('P=',s:4:2);
readln;
end.

while..do:

uses crt;
var i,n:longint;
s:real;
begin
clrscr;
write('nhap so n:');readln(n);
s:=1;i:=1;
while i<=n do
begin
 s:=s*i;
 i:=i+1;
end;
write('P=',s:4:2);
readln;
end.

(mong dc 5*+hay nhất)

a.

var n,i,s: integer;
begin
    readln(n);
    for i:=1 to n do s:=s+i;
    write(s);
    readln
end.

b.

var n,i: integer;
    s: real;
begin
    readln(n);
    for i:=1 to n do s:=s+1/i;
    write(s:2:2);
    readln
end.

c.

var n,i,p: integer;
begin
    readln(n);
    p:=1;
    for i:=1 to n do p:=p*i;
    write(p);
    readln
end.