De&Dap an Tin hoc

Bài 1
Var i,n:integer;
s:longint;
Function nt(a:integer):boolean;
Var b,dem:integer;
Begin
dem:=0;
For b:=1 to a do
if a mod b = 0 then dem:=dem+1;
if dem = 2 then nt:=true
else nt:=false;
End;
BEGIN
Write('Nhap N: '); Readln(n);
If ((n mod 2) <> 0) then
for i:= 2 to n do
if nt(i) then s:=s+i;
if n mod 2 = 0 then
for i:=1 to n do
if (i mod 2) <> 0 then s:=s+i*i;
Writeln('Tong S=',s);
readln;
END.
Bài 2
Var
i,j,k,n,x,y,z,dem: integer;
BEGIN
Write('Nhap so tien can rut ( n<= 10000): '); readln(n);
Write('Nhap 3 loai tien ma may co (x,y,z<=500) : '); readln(x,y,z);
For i:=0 to n div x do

for j:=0 to n div y do
for k:=0 to n div z do
if i*x +j*y +k*z = n then
begin
Dem:=dem+1;
Writeln('Cach ',dem,': So tien loai ',x,'; ',y,'; ',z,'; lan luot la:
',i*x,'; ',j*y,'; ',k*z,'.');
end;
if dem= 0 then Write('Khong co cach nao de rut dung so tien yeu cau')
else Writeln('Co tat ca ',dem,' cach rut tien');
readln;
END.
Bài 3
uses crt;
Var
i,t,k1,k2: integer;
j,g: char;
s1,s2: String;
BEGIN
Write('Nhap xau ky tu : '); Readln(s1);
For i:=1 to length(s1) do s1[i]:=Upcase(s1[i]);
For i:=1 to length(s1) do
For j:='A' to 'Z' do
Begin
if j=s1[i] then
begin
t:= (k1+5) mod 26;
k2:=0;
for g:='A' to 'Z' do
begin

if k2=t then s2:=s2+g;
k2:=k2+1;
end;
end;
k1:=k1+1;
end;
Write(' Xau ky tu tren duoc ma hoa la: ',s2);
Readln;
END.