[Godhimself]

Define the classes like so:

pawn Код:

#define CLASS_ONE
#define CLASS_TWO

Make a stock that seperates the team from AddPlayerClass, So the 1st AddPlayerClass will be 0, the 2nd 1 and so on.

pawn Код:

stock OnPlayerSelectClass(playerid, classid);
{
    switch(classid)
    {
        case 0:
        {
             gTeam[playerid] = CLASS_ONE;
        }    
        case 1:
        {
             gTeam[playerid] = CLASS_TWO;
        }
    }
}

And place the function under OnPlayerRequestClass(playerid, classid) like so:

pawn Код:

public OnPlayerRequestClass(playerid, classid)
{
    OnPlayerSelectClass(playerid, classid);
    //other code here
    return 1;
}

Should work.

EDIT: typos

EDIT2: typo