static LastWeapon[MAX_PLAYERS]; // Una variable que almacena la ъltima ID del arma.


public OnPlayerUpdate(playerid)
{   
    if(GetPlayerWeapon(playerid) != LastWeapon[playerid]) // Si cambiу de arma...
    {
        new const weapon = GetPlayerWeapon(playerid), new oldammo; 

        GetPlayerWeaponData(playerid, GetWeaponSlot(LastWeapon[playerid]), oldammo, oldammo);
        CallLocalFunction("OnPlayerWeaponChange", "dddii", playerid, weapon, LastWeapon[playerid], GetPlayerAmmo(playerid), oldammo);

        LastWeapon[playerid] = weapon;
    }
    return 1; 
}
 
forward OnPlayerWeaponChange(playerid, newweapon, oldweapon, newammo, oldammo);