loop function as used in workshop 6

In workshop 6, the use of the loop function is demonstrated through portfolio strategy:

while(asset(loop("EUR/USD","USD/JPY")))
while(algo(loop("TRND","CNTR")))
{
if(Algo == "TRND")
tradeTrend();
else if(Algo == "CNTR")
tradeCounterTrend();
}

on my screen ,in the tutorial, it appears that the second loop is not indented but since it won't work without indentation since the loops won't be nested I assume it is just a problem on my screen for some reason...

My real question comes after reading the loop function help file that states that the pointers/strings are returned in sequence on each successive call to the loop function and 0 when there are no arguments to loop upon. So, after the inner loop has done for "EUR/USD" and I move to "USD/JPY", why the inner loop function don't return 0? Why has it undergone a "reset" and returning the pointers in sequence again?
I understand it works but I don't understand why - since this function clearly retains its state between function calls I don't understand what makes it "rewind"?

Hopefully, someone can shed some light on this point.

Hi eval, it is correct what you say concerning the behaviour of the asset loop but also remember the behaviour of the run() function: it is called every bar. So, it is correct that the asset loop eventually return zero but it is called again at the next run() call to start with "EUR/USD" again, it is like a c program with main() that is restarted. Concerning the algo loop, it is restarted for each iteration of the outer loop, like in this c script



it prints 0 1 1 2 2 3 (0+0 0+1 1+0 1+1 2+0 2+1)

This is what happens in the first two bars:

First bar:

"EUR/USD" with "TRND"
then "EUR/USD" with "CNTR"
then the inner loop exits
then "USD/JPY" with "TRND"
then "USD/JPY"with "CNTR"
then the inner loop exits
then the outer loop exits

Then comes the second bar:

"EUR/USD" with "TRND"
then "EUR/USD" with "CNTR"
then the inner loop exits
then "USD/JPY" with "TRND"
then "USD/JPY"with "CNTR"
then the inner loop exits
then the outer loop exits

Feel free to ask if you have any doubt!

Hi eyal,

A few other things to realize to perhaps help clarify:

a) Indentation and other formatting is for us humans to help understand code. The computer doesn't care about indentation. Don't rely on it for understanding - it will sometimes mislead you!

b) In this code, the while(asset is the outer loop and the while(algo is the inner loop.

c) The outer while(asset loop contains only one statement - the while(algo. For this reason it doesn't need the {}.

d) As Mithrandir77 shows, the outer while(asset loop is first set to EUR/USD and then the inner while(algo loop executes - TRND, CNTR, 0. Then it's done, control returns to the outer while(asset, USD/JPY is set, the inner while(algo executes all over again as before, control again returns to the outer while(asset, 0 is set, and the looping is done.

HTH.

hi DdlV and Mithrandir77,

Thanks a lot guys - it really helped.

I am going to write some test scripts to see that I fully understand its use.

Eyal

You are welcome eyal! (I am blind or did you change your username? )

hi,

cool! no, did not change my username...