Expert Advisor Programming by Andrew R. Young

Advanced Order Placement
}
string ErrLog = StringConcatenate("Bid: ",Bid," Ask: ",Ask," Price: ",
PendingPrice," Lots: ",LotSize);
Print(ErrLog);
At the top, we include the stdlib.mqh file. We add the ErrorCode global variable to store our error
code. The OrderSend() places a buy stop order. If the function is not successful, our error handling
code is run.
First, we store the value of GetLastError() in ErrorCode. Then we call the ErrorDescription()
function, using ErrorCode as the argument. Next, we use the StringConcatenate() function to
create our alert message, which is stored in the string variable ErrAlert.
StringConcatenate() is an MQL function that allows you to create complex strings using variables
and constants. Each string element to be joined (or "concatenated") together is separated by a
comma. Try typing the examples above into MetaEditor to view it with syntax highlighting.
You can also concatenate strings by combining them with a plus sign (+). Using
StringConcatenate() is clearer and more efficient, but if you want to simply concatenate a short
string, use the plus sign to combine string constants and variables:
string PlusCat = "The current Ask price is "+Ask;
// Sample output: The current Ask price is 1.4320
The Alert() function displays a pop-up on the user's desktop, containing the contents of the
ErrAlert variable. Figure 3.2 displays the output of the Alert() function.
We construct another string with our price and trade parameters, and store it in the ErrLog variable,
which we pass to the Print() function. Print() prints the contents of the function argument to the
experts log. The experts log can be viewed from the Experts tab inside the Terminal window, or from
the Journal tab in the Tester window if you're using the Strategy Tester.
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