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Quick Programming Question

  • #1
  • First Post: Aug 25, 2009 3:05am Aug 25, 2009 3:05am
I have noticed that the following loop is widely and routinely used for counting, closing or deleting orders, etc:

Inserted Code
for (int i = OrdersTotal() [color=red]-1[/color]; i >= 0; i--)

My question is why do we use the -1 piece of the code? Is this logically correct while we want to include all orders in our search? Isn't this used only when searching for candles and we want to exclude the 0 candle?

Appreciate your clarification.
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  • #2
  • Aug 25, 2009 3:24am Aug 25, 2009 3:24am
let's say there are 10 orders for orderstotal. Although it would be human nature to count them 1 through 10, computers like to make things difficult and number them 0 through 9. So we subtract 1 to compensate for that.
  • #3
  • Aug 25, 2009 3:25am Aug 25, 2009 3:25am
The Orders array is a zero based array and the OrdersTotal is one based hence the need to subtract one.

So the first order in the list is not Order(1) but Order(0).

Make sense?

Lux
MT4 EA, Indicator and Alert Coder Since 2006
  • #4
  • Aug 25, 2009 3:48am Aug 25, 2009 3:48am
Quoting luxinterior
The Orders array is a zero based array and the OrdersTotal is one based hence the need to subtract one.

So the first order in the list is not Order(1) but Order(0).

Make sense?

Lux

Thanks for the quick reply both magnumfreak and luxinterior.

I happened to know that the numbering of orders in the list of active (market & pending) and closed orders starts with zero but to me if the total of the orders is 10 then with OrdersTotal()-1 the system should count from 8 to 0, ignoring the last order, not from 9 to 0.
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  • #5
  • Aug 25, 2009 5:14am Aug 25, 2009 5:14am
Quoting unaizams
Thanks for the quick reply both magnumfreak and luxinterior.

I happened to know [font=Verdana]that the numbering of orders in the list of active (market & pending) and closed orders starts with zero but to me if the total of the orders is 10 then with OrdersTotal()-1 [color=black]the system should count from 8 to 0, ignoring the last order, not from 9...
true if 10 - 1 = 8
  • #6
  • Aug 25, 2009 5:23am Aug 25, 2009 5:23am
Quoting unaizams
Thanks for the quick reply both magnumfreak and luxinterior.

I happened to know [font=Verdana]that the numbering of orders in the list of active (market & pending) and closed orders starts with zero but to me if the total of the orders is 10 then with OrdersTotal()-1 [color=black]the system should count from 8 to 0, ignoring the last order, not from 9 to...
example 5 orders index 0,1,2,3,4

5-1 = 4

countdown
4 3 2 1 0 = still 5 orders

see
http://www.codersource.net/c++_arrays_tutorial.html
Invincibility lies in the defence, the possibility of victory in the attack
  • #7
  • Aug 25, 2009 5:54am Aug 25, 2009 5:54am
OK, will it present a problem to the system if I do not subtract 1 or is it just to make the system more efficient?
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  • #8
  • Aug 25, 2009 6:03am Aug 25, 2009 6:03am
Quoting unaizams
OK, will it present a problem to the system if I do not subtract 1 or is it just to make the system more efficient?
its like this:

array[ index ] => value

array with 2 elements

array[0] => value1 or order1 or ...
array[1] => value2 or order2 or ...

sizeof array is 2

for( start, while, do )

for( i = 2; i >= 0; i-- ) ..... 2, 1, 0

but you dont have array[2] array with index 2

depending on the programming language, it will give you an error or a value from computer memory you dont need or want to, either way its better to start within the array, in this case you want to start from index 1 and count to zero, therefore you substract 1 from the size of the array (in this case 2)

so it looks like

for( i = size -1; i >= 0; i-- ) .... 1, 0 thats what you want
Invincibility lies in the defence, the possibility of victory in the attack
  • #9
  • Aug 25, 2009 6:35am Aug 25, 2009 6:35am
Thanks silverheat and thank you all others who responded.
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  • #10
  • Aug 25, 2009 6:35am Aug 25, 2009 6:35am
Quoting unaizams
OK, will it present a problem to the system if I do not subtract 1 or is it just to make the system more efficient?
Won't hurt anything.
  • #11
  • Aug 25, 2009 6:37am Aug 25, 2009 6:37am
... about efficiency

there is dynamic and static memory allocation, with static allocation as in c++ (i think mql is a c++ derivative and has also static allocation) the program works faster, because the size in memory is known at compile time.

the problem with starting outside the array, if you get an arbitrary value from memory, is, for example, if you sum up the values you get an undesired outcome.

for example, the programs stores data from an array with size 4, you want to sum up, in the next place in memory there is a value from another array

MEM 0011 -> VAL 5 (array_1[0])
MEM 0012 -> VAL 8 (array_1[1])
MEM 0013 -> VAL 1 (array_1[2])
MEM 0014 -> VAL 4 (array_1[3])
MEM 0015 -> VAL 5000 (array_2[0] )

starting from 4 to 0 you will get 5018, but your desired outcome is 18
Invincibility lies in the defence, the possibility of victory in the attack
  • #12
  • Aug 25, 2009 6:54am Aug 25, 2009 6:54am
Wouldn't it be nicer if the sbtraction process be built in the standard functions; OrdersTotal(), OrdersHistoryTotal, etc ?
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  • #13
  • Last Post: Aug 25, 2009 6:57am Aug 25, 2009 6:57am
Quoting unaizams
Wouldn't it be nicer if the sbtraction process be built in the standard functions; OrdersTotal(), OrdersHistoryTotal, etc ?
not really then if you actually wanted to know how many orders you had you would have to remember to add one
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