Nếu có gì không đúng thì bạn nói để mình sửa.
=====================================
18:
program Hello;
uses crt;
var n:string;
begin
readln(n);
writeln(length(n));
readln;
end.
=========================
19:
program Hello;
uses crt;
var n,a,s:int64;
begin
readln(n);
while n > 0 do
begin
a:= n mod 10;
n:= n div 10;
if a mod 2 <> 0 then
s:= s + a;
end;
writeln(s);
readln;
end.
=================================
20:
Theo mình thì vị trí chẵn bắt đầu từ 2;
program Hello;
uses crt;
var n,a,s:int64;
begin
readln(n);
while n > 0 do
begin
n:= n div 100;
a:= n mod 10;
s:= s + a;
end;
writeln(s);
readln;
end.
=======================================
21:
program Hello;
uses crt;
var n,a,s:int64;
begin
readln(n);
s:= 1;
while n > 0 do
begin
a:= n mod 10;
n:= n div 10;
if a mod 2 <> 0 then
s:= s * a;
end;
writeln(s);
readln;
end.
