THAM KHẢO:
uses crt;
var a,cv,dt:integer;
begin
clrscr;
write('a='); readln(a);
cv:=a*4;
dt:=sqr(a);
if a>0 then
begin
writeln('chu vi hinh vuong la: ',cv);
writeln('dien tich hinh vuong la: ',dt);
end
else writeln('vui long nhap so a lon hon 0');
readln;
end.