Expert Advisor Programming by Andrew R. Young

EXPERT ADVISOR PROGRAMMING
// Place near the end of the start() function
if(Debug == true) Print(StringConcatenate("Bid:",Bid," Ask:",Ask," MA:",MA,
" BuyTicket:",BuyTicket," SellTicket:",SellTicket));
The above code will log price and indicator information, as well as the contents of the BuyTicket and
SellTicket variables. If there are any questions about how a trade was opened, or why a trade was
not opened, the log at that particular moment will show the status of all relevant trade conditions.
You can turn logging on and off with the Debug external variable.
The debug Print() statement should be placed near the end of the start() function, after all
trading functions. If you are using a timer and/or an execute at bar open feature, place the debug
Print() statement inside the timer block so that it will only run when necessary. Otherwise, the
debug line will print to the log on every tick, which can result in a large log file.
Fixing Compilation Errors
When you compile your expert advisor, the compiler will check for correct syntax, and ensure that all
custom functions and variables have been properly declared. If you've left something out, the
compiler will stop, and any compilation errors will appear in the Errors tab in the Toolbox window.
When confronted with a long list of compilation errors, always start with the first one. Double-click
the error in the list, and the editor will jump directly to the line with the error. Correct the error and
recompile. Sometimes a simple syntax error will result in several unrelated errors, although only the
first one was valid.
Here is a list of common compilation errors and their solutions:
• Variable not defined – You forgot to declare a variable with a data type. If it is a global or
external variable, declare it at the top of the file. If it is a local variable, find the first
occurrence and place the data type declaration in front of it. Otherwise, check the spelling or
the case (upper/lower) of the variable name.
• Variable already defined – You declared the same variable twice. Remove the data type
declaration from all duplicate variable declarations.
• Function is not defined – If the function in question is in an include or library file, be sure
that the #include or #import directive is placed at the top of the file and is correct.
Otherwise, check the spelling or the case of the function name, and be sure that it exists
either in the current file or in the relevant include or library files.
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