error 017: undefined symbol "playerid"

#include <a_samp>
new gate;
new bool:gateopen;

public OnFilterScriptInit() // Alternatively, use OnGameModeInit if you implement it in your gamemode
{
    SetTimer("GateCheck", 800, true); //This is used to create the timer. The "GateCheck" is the callback we'll be using,
    // the '800' is the amount of milliseconds between each call and the 'true' indicates that this timer is looping endlessly
    gate = CreateObject(969,1801.19995117,-1720.90002441,12.50000000,0.00000000,0.00000000,178.00000000);
    //'gate = CreateObject(...);' = Assigns the object id of the gate to the 'gate' variable
    //16442 = object model id < change it to the model id you use for your gate
    // 8.0, 3.0, 10.0 = coordinates of the gate
    // 0.0, 0.0, 0.0 = Rotation of the gate. None in this case.
    return 1;
}

forward GateCheck();
public GateCheck()
{
    for(new i; i < MAX_PLAYERS; i++) // Start the loop
    {
            if(IsPlayerInRangeOfPoint(i , 15.0, 8.0, 3.0, 10.0)) //Check if any player is in the area. Replace '8.0, 3.0, 10.0' with your own coordinates of your closed gate.
            {
                if(gateopen == false) // If the gate isn't open...
                {
                    MoveObject(gate, 1801.19995117,-1720.90002441,12.50000000,0.00000000,0.00000000,178.00000000); //Then open it! Change '32.0, 12.0, 10.0' to the coordinates of your opened gate.
                    gateopen = true; // Setting this to true indicates it's open(ing)
                }
            return; //This closes the callback
            }
    }
    //This is called if nobody has been found near the gate. Obviously, because 'return' would fully close the function and this wouldn't be used then.
    if(gateopen == true) //If the gate IS open, but there's no one near..
    {
            MoveObject(gate, 1807.80004883,-1721.30004883,12.50000000,0.00000000,0.00000000,178.00000000); // Change the '8.0, 3.0, 10.0' to the coordinates of your gate when it's closed.
        gateopen = false; //This indicates the gate is closed again. Or at least, closing.
    }
}