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![Processing of trade events in Expert Advisor using the OnTrade() function](https://c.mql5.com/2/0/function_ontrade_MQL5.png)
MQL5 gave a mass of innovations, including work with events of various types (timer events, trade events, custom events, etc.). Ability to handle events allows you to create completely new type of programs for automatic and semi-automatic trading. In this article we will consider trade events and write some code for the OnTrade() function, that will process the Trade event.
![OOP in MQL5 by Example: Processing Warning and Error Codes](https://c.mql5.com/2/0/mistake.png)
The article describes an example of creating a class for working with the trade server return codes and all the errors that occur during the MQL-program run. Read the article, and you will learn how to work with classes and objects in MQL5. At the same time, this is a convenient tool for handling errors; and you can further change this tool according to your specific needs.
![How to call indicators in MQL5](https://c.mql5.com/2/0/Calling_indicators_MQL5.png)
With new version of MQL programming language available not only the approach of dealing with indicators have changed, but there are also new ways of how to create indicators. Furthermore, you have additional flexibility working with indicator's buffers - now you can specify the desired direction of indexing and get exactly as many indicator's values as you want. This article explains the basic methods of calling indicators and retrieving data from the indicator's buffers.