no return value of call procedure mysql - mysql

Question

I have a procedure in mysql and it has 4 parameters as Input and 3 parameters of OUTPUT and one param of OUTPUT doesn't return nothing (null).
DELIMITER $$
drop procedure if exists `cierreMes`$$
create procedure cierreMes (in tarjeta varchar(100),in bancoBus varchar(100),in mes int,in anyo int, out total int, out nulas int, out erroneas int)
begin
declare stockActual int default 0;
declare cantidad int;
/*declare xcantidad,xnulas,xerroneas int;*/
declare entrada, salida int default 0;
declare total int default 0;
select stock
into stockActual
from almacen
where idProducto =
(select idProducto from productos where productos.banco = bancoBus and productos.plastico = tarjeta);
call entradasSalidas(tarjeta,bancoBus,mes,anyo,#ent,#sal);
set entrada = #ent;
set salida = #sal;
call obtenerMovimientosMes(tarjeta,bancoBus,mes,anyo,#cant,#nul,#err);
set cantidad = #cant;
set nulas = #nul;
set erroneas = #err;
set total =(stockActual + entrada) - (salida + cantidad);
select total;
end$$
DELIMITER ;
call cierreMes('4B MC','SANTANDER',3,2013, #total, #nulas, #erroneas);
select #total, #nulas, #erroneas;
When i do "call" #nulas and #erroneas return a value, but #total
nothing.
With select total, its works fine. but no returns a value, in this select : select #total, #nulas, #erroneas; #total is null.

Answer 1

You calculate total with this formula:
set total =(stockActual + entrada) - (salida + cantidad);
If one of the values used in the calculation is NULL, then total will be NULL.
I can see set statements for entrada, salida, and cantidad. But what is the value of stockActual?
It seems you are missing a statement that will set the value of stockActual.