Please contribute more to what you need.

For simplicity, I'll write you here the steps, so that you can apply them to MQL4 and MQL5 codes:

For MQL5

1) First step, put these 2 lines at the beginning, close to the global variables:

double capitalToCompound = AccountInfoDouble(ACCOUNT_BALANCE);
         input bool      compounding            =      true; // Compounding

2) Second step, put these lines in OpenPosition function just before ManageOrderSend, and replace "EntryAmount" with "amount" variable in the ManageOrderSend function.

double amount = Entry_Amount;
   if(compounding && capitalToCompound > 0) amount = Entry_Amount*(AccountInfoDouble(ACCOUNT_EQUITY)/capitalToCompound);
   amount = NormalizeDouble(amount,2);

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For MQL4, the procedure is similar; the first step is identical to the MQL5.
The second step is basically modifying the "amount" variable, here's the code:

if(compounding && capitalToCompound > 0) amount = Entry_Amount*(AccountInfoDouble(ACCOUNT_EQUITY)/capitalToCompound);
   amount = NormalizeDouble(amount,2);

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It's not necessary to initialize the "capitalToCompound" variable in OnInit, because it's already initialized in the global variables when created.

....this is it! How to embed the "Compounding Effect", fully explained!

...Enjoy!