I am a beginner , What conditional must use magic number? How to use magic number?

[陳柏昌]

I am a  beginner , What conditional must use magic number? How to use magic number? 

[Marcus]

//Setting up the Magic Number

input ulong  Magic_Number = 1234567890; //Magic Number

int OnInit()
  {
   trade.SetExpertMagicNumber(Magic_Number);
   return(INIT_SUCCEEDED);
  }

//Getting Position Magic Number so that EA only alters/close positions it opened.

for(int i=PositionsTotal()-1; i>=0; i--)

   {

    ulong Position_Magic_Number = PositionGetInteger(POSITION_MAGIC);

    if(Position_Magic_Number == Magic_Number)

       {

       //Actions for positions that only the EA has opened

       }

  }

[Sergey Golubev]

MagicNumber: "Magic" Identifier of the Order - the article (MT4)

[The Huy Phan]

陳柏昌:
I am a  beginner , What conditional must use magic number? How to use magic number? 

Magic number is a number for 1 EA, to define the oders of that EA!

If you use a few EAs on 1 platform, you have to define the different magic number for each EA!

[Mulyanto Gunawan]

陳柏昌:
I am a  beginner , What conditional must use magic number? How to use magic number? 

Magic Number comparison is the way to go. you should use Order Comment comparison only if your EA actually writes different comments for different trading situations and you wanna have it to have different actions for such cases.

Good luck !

[William Roeder]

陳柏昌:  What conditional must use magic number? How to use magic number? 

Using OrdersTotal directly and/or no Magic number filtering on your OrderSelect loop means your code is incompatible with every EA (including itself on other charts and manual trading.)
          Symbol Doesn't equal Ordersymbol when another currency is added to another seperate chart . - MQL4 programming forum
          MagicNumber: "Magic" Identifier of the Order - MQL4 Articles