What is an Expert Advisor?

What is an Expert Advisor?

An expert advisor (or expert adviser, EA, trading robot...) is an automated trading program written in MQL programming language.

Expert advisors (commonly abbreviated as EA) can place, modify and close orders according to a trading system algorithm. EA’s generally use indicators to generate trading signals. These indicators can be the ones that come with MetaTrader, or they can be custom indicators.

An indicator is a technical analysis tool that calculates price data to give an interpretation of market activity. An indicator draws lines or objects on the chart. Indicators cannot place, modify or close orders. Examples of indicators include the moving averages,Heiken Ashi or stochastics.

A script is a simplified expert advisor that performs a single task, such as placing a pending order or closing all orders on a chart. A few useful scripts are included with MetaTrader.

MetaEditor (for programmers)

MetaEditor is an Integrated Development Environment (IDE) for MQL that comes packaged with MetaTrader. It includes useful reference, search and auto-complete tools that makes coding in MQL alot easier.

Variables

A variable is the basic storage unit of any programming language. Variables hold data necessary for our program to function, such as prices, settings and indicator values. Variables must be declared before they are used. To declare a variable, you specify it’s data type, an identifier, and optionally a default value. If you declare a variable more than once, or not at all, you’ll get a compilation error. The data type specifies the type of information the variable holds, whether it be a number, a text string, a date or a color. Here are the data types in MQL:

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