How can I do for retrive a value from a store procedure from a sql 7.0 stored procedure

example

SQL 7.0 Store Procedure****

Create procedure sp_calculo @valor int,
@fecha datetime,
@valor_retorno int output as
begin
insert transaccion (valores,fechas)
values(@valor,@fecha)

select @valor_retorno = @@identity

return

end

VFP program for get the @valor_retorno value

a=sqlconnect("coneccion")
if a>0
b=sqlprepare(a,"exec sp_calculo 10,[01/01/1999] ","mycursor")
c=sqlexec(a)
else
wait window "Error de Conexion"
endif

this do not work bacouse i have not the @valor_retorno

what is bad or how can I do for get the return value, please help me