Expert Advisor Programming by Andrew R. Young

Tips and Tricks
// Global variables
string GlobalVariablePrefix;
int init()
{
GlobalVariablePrefix = Symbol()+Period()+"_"+"ProfitBuster"+"_"+MagicNumber+"_";
}
We use the current symbol and period, along with an identifier for the EA and the MagicNumber
external variable. Now, when we set a global variable using GlobalVariableSet(), we use the
prefix that we defined above, along with the actual variable name:
GlobalVariableSet(GlobalVariablePrefix+Counter,Counter);
So if we're trading on EURUSD on the M15 timeframe with an EA named "ProfitBuster", using 11 as
our magic number and Counter as our variable name, the name of our global variable will be
EURUSD15_ProfitBuster_11_Counter. You can use any convention you wish for naming your global
variables, but including the above information is strongly recommended.
To retrieve the value of a global variable, use the function GlobalVariableGet() with the variable
name as the argument:
Counter = GlobalVariableGet(GlobalVariablePrefix+Counter);
To delete a global variable, use the function GlobalVariableDel() with the variable name as the
argument. To delete all global variables placed by your EA, use the function
GlobalVariableDeleteAll() with your prefix as the argument.
GlobalVariableDel(GlobalVariablePrefix+Counter);
GlobalVariableDeleteAll(GlobalVariablePrefix);
For more information on global variable functions, see the Global variables topic in the MQL
Reference.
Check Order Profit
Sometimes it may be useful to check the current profit on an order, or to check the total profit on an
order that has already closed. There are two ways to check profit. To get the profit in the deposit
currency, use the OrderProfit() function. You must first select the order using OrderSelect().
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