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First of all, this discussion group (and the software) is GREAT.
It's so encouraging that such a group of like-minded people
exist.
As soon as I'm up to speed with AFL, I will make sure to
contribute in any way that I can.
Anyway, I'm just starting out with AFL and I'm having trouble
getting my head around a few basic concepts. I should say that
I've been programming for 15 years, but that obviously hasn't
helped me here!
I've trawled through the historical discussions and also read the
help files, etc, but I still can't seem to grasp the language
properly.
Here are my questions…
1. Boolean Expressions
I'm trying to write an Automatic Analysis Script (sorry, I
don't know the correct technical term for this) for issuing buy
and sell signals.
I understand that I need to initiate a `Buy' signal by
assigning a `True' Boolean expression to the implicit
`Buy'
variable such as this…
Buy = Close[15] > MA(Close,50);
I think I have understood this concept, but please correct me if not.
However, what I can't grasp is why AFL considers the above
Boolean expression to be valid in the given scenario, but it does NOT
consider it to be a valid Boolean expression in the following
scenario…
if ( Close[15] > MA(Close,50) )
Buy = 1;
For this `If' statement, I am given the following error…
Error 3.
Condition in IF, WHILE, FOR statements
has to be Numeric or Boolean type.
You can not use array here,
please use [] (array subscript operator)
to access array elements
Can somebody explain to me why AFL considers the same expression to
be a valid Boolean expression in the first example but not the second?
2. Previous Closing Price
How do I retrieve the closing price for 15 bars ago? I want to
say… "Is this closing price of 15 bars ago greater than the
50 day moving average of today's bar?"
I appreciate that the code I've given so far is clearly wrong
because the it's using the index 15 (i.e. Close[15]). What I
want to do is something like this…
If ( Close[CurrentBar – 15] > MA(Close,50) )
But I can't figure out how to get a handle to the index of the
current bar so that I can subtract 15 from it?
3. Boolean Functions
How do I write a Boolean function?
I want to write something like this…
function myBooleanFunction()
{
myReturnValue = 0;
if ( expression )
if ( expression )
if ( expression )
myReturnValue = 1;
return myReturnValue;
}
if ( myBooleanFunction() == 1 )
Buy = 1;
else
Sell = 1;
Is this the correct way to write and use a boolean function?
Thanks for your help
Arold
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