The present invention relates to a system for managing a game by random comparison among basic data stored in a memory and data instantaneously inputted with a point of sale. More specifically, the invention concerns a system of the above kind allowing managing a game with prize allotment by POS or other analogous system directly at the desk. As it is well known, in the recent years many competitions have been proposed relevant to the allotment of prizes by random drawing, said competitions being controlled in a more or less automatic way. In this field, the Applicant has realised a system for managing an innovative game that has required the realisation of an innovative and specific system. The solution according to the present invention allows managing a game directly with the point of sale, for example the supermarket, the hypermarket, ecc, said game providing the drawing of one or more articles from the group of those comprising the assortment of the point of sale. The drawn articles are then compared directly at the desk with those purchased by the client and, in case one or more drawn articles is present among those purchased, the client receives a prize, for example corresponding to the amount of the shopping presented at the desk. It is therefore specific object of the present invention a system for managing a game by random comparison among basic data stored in a memory and data instantaneously inputted with a point of sale, said system comprising a central u nit and at least one peripheral unit, said central unit being provided with a program for managing the game and interfacing with at least one desk, said at least one peripheral unit being provided with interaction means for activation by the client, and interfaced with the central unit. Preferably, according to the invention, a plurality of peripheral units is provided. According to the invention, said central unit provides a server, in which the game managing program is installed. Particularly, said game managing program provides a module for controlling communication with peripheral units, a module for controlling the communication with the system for managing desks, a module for controlling the game, with drawing of product references, comparison with shopping of the client, determination of the prize, managing of jackpot, a manager report module, a module for controlling database with references of point of sale, necessary for drawing of articles, a module for controlling manager report database, containing events concerning stakes, wins, statistical data and any other information deemed necessary. Furthermore, according to the invention, said central unit can be provided with a GPRS adaptor or similar telecommunication system, on the basis of the state of the art and the availability of the service in the specific location (GSM, UMTS, ecc.) or with a standard phone connection. Still according to the invention, each peripheral unit provides a button and at least one among a display, preferably an LCD display, a printer, preferably a thermal matrix printer, a smart card reader or electronic key reader and voice synthesiser. Particularly, said button is transparent with an inside light, or it is coloured. The button can be further mounted directly on the peripheral unit, or it can be provided on a graspeable support connected with the basic apparatus by an extensible cable. Display could be of the "touch screen" type, in this case the button being comprised by an icon on the screen. Furthermore according to the invention, the system according to the invention manages a game providing the following phases: - reading of articles chosen by the client by the scanner provided with the desk; - transmission of the code read by the scanner at the desk, the desk transmitting the code to the server; - opening by the managing system of a request for the new receipt, with summing of articles that have been really purchased when they are read or after the end of the selling; - calculation and display of the shopping value both on the desk and on the display of the peripheral unit, with updating of the quota of the stake after each modification or at the end of the selling;; - asking the client if he/her wishes playing, indicating on the display of the peripheral unit the cost of the stake; - if the client accepts playing, the system is activated, preparing the same for the stake, by pushing a button of the desk, said button being suitably programmed by an authorisation mechanism connected to the peripheral unit; - interaction of the client with the peripheral unit; - instantaneous random drawing by the system from the assortment of articles of the point of sale, stored in the database, of a certain programmable number of articles; - comparison of extraction with purchased articles: if the programmed number of articles is present among those drawn, the client wins the shopping; if a further number of articles, always programmed and higher than the previous one, is present, the Client beside the shopping, wins tickets corresponding to the jackpot accumulated until that moment; otherwise the client losses; - charge the cost to the client. In the following, a particularly preferred embodiment of the system according to the invention will be described along with its operation. Peculiar characteristics of the system suggested according to the invention are those necessary for managing a game wherein: - the player personally makes stake, in this case the client of the point of sale, by interaction with a button or similar interface; - player is informed, before the stake, about the amount that he/she plays, for example corresponding to a percentage of the total amount of the shopping; - sum played by the client is directly charged on the receipt at the desk, after the client has accepted the stake; - system is easily installable, cheap, it can be remote controlled and gives information about the stakes, the prizes win, ecc; - stakes are directly awarded to the desk operator, so that an encouraging to the promotion of the same is obtained; - it is possible "set aside" a part of stakes in a "jackpot"; - stake collection system, i.e. that part available for the client, can be substantially similar to that of a traditional "flipper apparatus"; interface lightens, emits sounds, ecc. System according to the invention is provided with a central unit and different peripheral units, although in line of principle it could also be comprised of single unit with interface (i.e. each desk has its own game). In any case, in the following the solution relevant to a system with a central unit and a plurality of peripheral units will be described. Said peripheral units are placed with the single desks, and are provided with a button, or other kind of interaction element, some lamps, an LCD display, a thermal matrix printer, a smart card reader or electronic key and a voice synthesiser. Furthermore, peripheral units are provided with a network interface (preferably a wireless interface in order to take into account of the installability simple requisite), controlled by a micro programmed circuit. Each peripheral unit will be housed inside a container with suitable, reassuring and pleasant shape and colours. Button is transparent, and is provided with an inside lightening, red coloured, and it lights when the apparatus is activated and ready for the stake. It is mounted directly in the peripheral unit, or it is mounted on a graspable support connected with the basic apparatus by an extensible cable, and it must be pushed to activate the game. Display is placed on the front portion of the peripheral unit, and it can display advertising messages and slogan when the peripheral unit is not activated, and the total amount of the shopping, the amount of the stake and the amount of the jackpot when acquiring the data, and information about the stake outcome. In the described embodiment, it is a 14x18 monochromatic or colour TFT backlit display. Preferably the printer is a chemical paper printer, provided inside the peripheral unit, giving a receipt indicating the stake, coming out from a front slot. Smart card or electronic key reader is placed behind the peripheral unit allowing the reading of a smart card (or of an electronic key) from which the system extracts the code of the operator of each desk given by the installer of the system. Detected code is transmitted to the server and associated to the stake. This will allow to the manager of the point of sale, when studying the system, to known the work of each single desk. In case sounds are emitted, an audio reproduction unit is provided. Said micro programmed control unit is further able controlling a certain number of LED in order to obtain light effects. Coming now to describe the central unit, it is comprised of a server, in which the system managing the game is installed. Said system is comprised of an assembly of software modules, each of them realising specific functionality of the system. The minimum configuration of the system for managing the game will provide the following sub-systems: - system for controlling communication with peripheral units; - system for controlling the communication with the system for managing desks; - system for controlling the game, with drawing of product references, comparison with shopping of the client, determination of the prize, managing of jackpot; - manager report system; - system for controlling database with references of point of sale, necessary for drawing of winning articles; - system for controlling manager report database, containing events concerning stakes, wins, statistical data and any other information deemed necessary. Central unit is provided with GPRS adaptor (or equivalent system) for allowing the access from outside to the managing and statistical data, loading of system updating, tele-assistance, ecc. Wireless adapter (for allowing connection in a local network of the peripheral units, an adapter for Ethernet network for interfacing with system for controlling the desks). As to the system for interfacing with the desks, different solutions are already available from the market leaders (IBM, NCR, MWCR) based on different hardware and software architectures. In the solution suggested according to the present invention, it has been realised an interfacing (necessary since for assigning the prize it is required knowing the total value of the shopping and the purchased articles) with systems based on PC server desks. These systems provide the use of a desk managing program working on a server, usually comprised of a personal computer. System will be installed with the point of sale, the central unit being provided with the back-office or with the central desk, and in any case close to the system controlling the desks. Peripheral units will be provided with the single desks, the application being realised in order to take into consideration the environment (kind of desks, operation parameters) ecc. Application will be initialised with data of the selling point references. When the client goes to the desk, cashier starts passing articles on the scanner. Scanner transmits the read code to the desk that transmits the same to the server. Now the code is taken by the managing system, opening a request for a new receipt. When new articles are read, it sums really purchased articles. At the end, value of shopping is calculated and displayed both on the desk and on the peripheral unit display. For each variation, the amount of the stake is kept updated, said amount corresponding to a percentage of the total amount of the shopping (2%). Now, cashier asks the client if he/she wishes playing, indicating on the peripheral unit display the amount of the stake. If the client accepts, cashier activates the system preparing it for the stake, pushing the button of the desk, which is suitably programmed. When the client pushes the button, the system instantaneously randomly draws a given programmed number of articles from the assortment of the point of sale and present in its database now, a comparison with purchased articles is made. If the programmed number of purchased articles is present among those purchased (for example 3 out of 20), the client wins the shopping. If a further number of articles, always programmed and higher than the previous one (6 out of 20), is present, the Client besides the shopping, wins tickets corresponding to the jackpot accumulated until that moment. Otherwise the client losses. The sum corresponding to the stake is automatically charged on the receipt both in case of win and of loss. A part of the stake, in case of loss, is summed to the jackpot. In case of win, amount of shopping is deduced by a 100% discount. Amount of stake is in any case charged to the client. The present invention has been described for illustrative but not limitative purposes, according to its preferred embodiments, but it is to be understood that modifications and/or changes can be introduced by those skilled in the art without departing from the relevant scope as defined in the enclosed claims.