Expert Advisor Programming by Andrew R. Young

Tips and Tricks
You can use the account functions AccountName(), AccountNumber() and AccountBroker() to
check the account name, number and broker respectively. Limiting usage by account number is a
common and easy to implement method of protection:
int CustomerAccount = 123456;
if(AccountNumber() != CustomerAccount)
{
Alert("Account number does not match!");
return(0);
}
You can use AccountName() or AccountBroker() in a similar manner. For AccountBroker(), you'll
first need to use a Print() statement to retrieve the correct return value from the broker. This value
will be printed in the experts log.
If you do decide to sell an EA commercially, be aware that MQL files are notoriously easy to
decompile. There are various methods you can use to make it more difficult for hackers to crack your
EA, such as placing functions in external libraries or DLLs. But ultimately, there is little protection
against a determined cracker.
MessageBox()
So far in this book, we've been using the built-in Alert() function to display error messages. But
what if you want to customize your alert dialogs, or request input from the user? The MessageBox()
function will allow you to create a custom pop-up dialog using Windows API functions.
To use the MessageBox() function, we must first #include the WinUser32.mqh file that is installed
with MetaTrader. This file imports functions from the Windows user32.dll file and defines constants
necessary for the MessageBox() function to work. Here is the syntax for the MessageBox() function:
int MessageBox(string Text, string Title, int Flags);
To use the MessageBox() function, we must define the Text to appear in the pop-up dialog, along
with a Title that appears in the title bar. We will also need to specify Flags that indicate which
buttons and icons should appear in our pop-up. If no flags are specified, an OK button will be the
default. Flags must be separated by the pipe (|) character.
Here's an example of a message box with Yes/No buttons and a question mark icon:
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