In order to connect the library to an EA it is necessary to make the following changes:

1. Insert the compiler directive before the declaration of functions:

#include <a-SimpleTrailing.mqh>

2. Declare the global variables:

color clModifyBuy = Aqua;    // Color of Buy modification icon
color clModifySell = Tomato; // Color of Sell modification icon

3. Declare the external parameters:

// Use sound signals during the execution of trades
extern bool   UseSound        = True; 
extern string NameFileSound   = "expert.wav"; // Name of the sound file
extern int    NumberOfTry     = 3;  // Number of trade attempts on errors 
extern int    PauseAfterError = 75; // Pause between trade attempts in seconds

4. Insert the line at the end of the start() function:

if(UseTrailing) 
    TrailingPositions();

5. Place the library file a-SimpleTrailing.mqh into the terminal folder ...\experts\include\

Once the library is connected, the EA will have the following external parameters:

// Use trailing stop. If 'False', the trailing stop is disabled.
UseTrailing = True;
// Trail only profit. If 'False', then the trailing stop will start 
// working in the unprofitable zone.
ProfitTrailing = True; 
TrailingStopBuy = 50;  // Trailing stop size for Buy orders.
TrailingStopSell = 50; // Trailing stop size for Sell orders.
TrailingStep = 5;      // Trailing step.

The TrailingPositions() function can take on the following parameters:

- symbol name ("" - current symbol);
- operation (-1 - any position, 0 - Buy, 1 - Sell);
- MagicNumber (-1 - any magic number).

This allows to narrow the scope of the trailing stop operation. For example, trail only Euro:

if(UseTrailing) 
    TrailingPositions("EURUSD");

Or trail only Pound Sells:

if(UseTrailing) 
    TrailingPositions("GBPUSD", OP_SELL);

And if the EA uses a magic number, then it must be passed to the maintenance function:

if(UseTrailing) 
    TrailingPositions("", -1, MAGIC);