Placing orders and managing positions

An EA acts on the market by sending trade requests. In MQL5 the simplest and safest way is the standard-library CTrade class, which wraps the lower-level request structures.

Using CTrade

#include <Trade/Trade.mqh>
CTrade trade;

void OpenLong()
{
    double ask = SymbolInfoDouble(_Symbol, SYMBOL_ASK);
    double sl  = ask - 200 * _Point;   // stop loss
    double tp  = ask + 400 * _Point;   // take profit
    trade.Buy(0.10, _Symbol, ask, sl, tp);
}

Buy and Sell open positions; PositionClose closes them; PositionModify adjusts stop loss and take profit. Always check the return value — a request can be rejected for many reasons.

Market vs pending orders

• Market order — execute now at the current price (Buy / Sell).
• Pending order — execute later when price reaches a level: BuyLimit, SellLimit, BuyStop, SellStop.

The netting vs hedging trap

MT5 accounts use one of two position models:

• Netting — one net position per symbol. A buy on top of a short reduces or flips the existing position.
• Hedging — multiple independent positions per symbol are allowed.

Your EA's logic must match the account mode, or a second order will not do what you expect. Always check before assuming you can hold opposing positions.

Things that bite real EAs

• Stops level — brokers reject stops placed too close to price (SYMBOL_TRADE_STOPS_LEVEL).
• Lot constraints — volume must respect the symbol's min, max and step.
• Requotes and slippage — the fill price can differ from what you requested; never assume an exact fill.
• Error handling — inspect trade.ResultRetcode() and react, rather than firing orders blindly. A robust EA assumes requests can fail and handles it.