EA that will trade multiple pairs

[BlueMoon]

When there is an intention to trade an EA on multiple pairs, I noticed that there are 2 ways to do this:

1. You create the EA and just run it on all the charts that you want it tun it with unique magic numbers.

2. You create an EA that will take the input of all pairs you want to trade and just run the EA on 1 chart.

The first way is easy but the 2nd way has many challenges. I wanted to find out if any of you use the 2nd type currently and wanted to get some ideas on how do you manage to separate the variables of each trade or each pair that are going to make trading decisions in the EA? I usually attempt to do that and most of the time I just get lost and confused and it becomes very complex and just end up with Option 1 where I just run it on the pairs I need to run it on.

The problem now that I face is that I want to create an EA that will run for all 28 pairs but also will have like 5 unique trades which will need to have variables assigned to each of these 28*5 trades open at any moment in time and my EA will need to make trading decisions on the values of these variables. So I am all confused on how do I even get started with this design?

Any one experienced in created something similar? I would really appreciate your input and ideas for the same.

[miro1360]

with arrays it is possible, but avoid it if possible and use one EA for one Pair...
... for few reasons, in MT4 opening multipairs can not be tested in tester, only in MT5 ... and only blocks in onTick section .... on Timer section is not working in tester
... in MT4 you can test reading data from other pairs, but not opening multipair trades

if it is not possible to avoid, than create it
... if you create it in onTick section, all your pairs depends on ticks from pair (from chart) where EA is placed (good or bad? it depends on your strategy)
... if possible, create and test your strategy in forward demo with blocks placed in onTimer section ... set timer interval for some reasonable value, like 10s (here again, it depends on your strategy)

... in overall, if you create multipair EA, and your strategy is lossable in lets say 5 pairs, in other pairs is most probably lossable too, ... when you sum that, you end up logically in the loss

... my hint is, focus for only few pairs (filter them too, because some pairs are more trendy (gbpjpy) and other pairs are more side (eurchf)
... create profitable EA for one pair (you can read data from other pairs) but with EA open only 1 pair based on that data ... read these data with multicurrency custom indicator if possible, if not possible you can do it in EA ...

working with multipair (or multicurrency) EAs is possible, be aware because it is big challenge and you can easily fail, your EA can fail and when you ended up with 28*x opened trades, you will easily lose yourself and probably a lot of money too (because closing 28 trades may not be cheap ) ...

[BlueMoon]

Thank you very much for taking the time to explain. I was also leaning towards just writing the EA for a single pair and just run it multiple times and avoid all the array and variables complications the the EA.

Thanks again.