procedure TPrincipal.ImporteKeyPress(Sender: TObject; var Key: Char);
var
numeros: set of '0'..'9';
i:integer;
begin
Try
numeros:=['0'..'9'];
i:=pos(',',importe.Text);
if (key ='.') and (i<0) then
begin
key:=',';
end
else
if not (key in numeros) and (key <> #8) then
key:=#0;
except
end;
end;