Im not getting the expected result

[anda_skoa]

in the part of this code I expect the variable precioFinal ( " precioFinal += costoFinal; " ) to acumulate all the costs of all the buyed items

Are you talking about the code in Factura:rocesar()?
Why would you expect that to hold a sum?
You are setting the variable to 0 on every call.

Cheers,
_