i need to create a function MarketPosition in Amibroker, just like the one in MultiCharts. description in MultiCharts:
MarketPosition(N) returns whether the strategy is currently flat, short, or long on the current bar or for
N closed positions ago. MarketPosition return values are:
-1 for a short position.
1 for a long position.
0 for flat (no position).

I want to create same kind of function in Amibroker, but not good enough at coding.
Can somebody please help me do this.

This thread is old, but it's a classic so I answer it as it could be useful for other people.

Use the Flip() function. In the following I assume you have defined your system using variables Buy/Sell/Short/Cover.
If one of them is not defined, assign 0 to it e.g if you have no short position:

 

Code

Short = Cover = 0; // no short positions

Now here's the solution to your problem:

 

Code

MarketPosition = Flip(Buy, Sell) - Flip(Short, Cover);

Yes, it's a one-liner, that's the magic of AFL.