4/ Vòng lặp vô tận vì biến $a$ không được khai báo.
1/
uses crt;
var A:array[1..1000] of integer;
i,n,tong:integer;
begin
clrscr;
write('Nhap n: '); readln(n);
for i:=1 to n do
begin
write('Nhap phan tu thu ',i,': ');
readln(A[i]);
if A[i] mod 2 = 0 then tong:=tong+A[i];
end;
writeln;
write('Tong cac so chan la: ',tong);
readln
end.
2/
uses crt;
var A:array[1..1000] of integer;
i,n:integer; tich:longint;
begin
clrscr;
write('Nhap n: '); readln(n);
tich:=1;
for i:=1 to n do
begin
write('Nhap phan tu thu ',i,': ');
readln(A[i]);
tich:=tich*A[i];
end;
writeln;
write('Tich la: ',tich);
readln
end.
3/
uses crt;
var A:array[1..1000] of integer;
i,n,tong:integer;
begin
clrscr;
write('Nhap n: '); readln(n);
for i:=1 to n do
begin
write('Nhap phan tu thu ',i,': ');
readln(A[i]);
if A[i] mod 2 = 1 then tong:=tong+A[i];
end;
writeln;
write('Tong cac so le la: ',tong);
readln
end.