It is really hard (or may be impossible) to build a winning strategy on this theory. Theory of probability was initially developed for the military purposes, and its calculations helped to hit the target more efficiently. But soon after its launch many gamblers have realized that this theory can be also applied in their field. All the numbers that occur in the game are controlled by a change and pure luck so probability theory can also be applied here. A great number of different calculations was made for all kinds of gaming especially for games like roulette craps and blackjack. In these games chances to win depend highly on numbers that occur during the game. But the most important thing about these games is that the player knows all the previous numbers - and that can help in calculations according to theory of probability.
In games like roulette craps or blackjack certain numbers can occur with certain probability (that principle works in many other games), but all the previous numbers can change this probability. But what is more interesting is that you can calculate this new probability. So does it mean that you can take some sort of computer, go to a casino and win all these games? In fact it is not that simple. All the laws of theory of probability work in a long run. It means that you have plenty of time. But can you imagine such a thing in a real life? Well... I guess not. So what is the answer: whether you can beat casinos in games like roulette craps or blackjack and whether there is an effective roulette or craps system? Yes, there is a system and it works fine but in order to win with it you need a lot of time - not a single day, not a week.
This time needed to win can be even longer than your life. So it is probably impossible to beat all the casinos with 100% guarantee. But as long as all these theories are real and effective you can slightly improve your chances to win. It doesn't matter if you are using the best computer in the world or making all the possible calculations, still the main thing that leads to winning is time.
So what is the conclusion of all this above said: do not believe a person who says that with his/her craps system (or any other gaming system) you can beat all the casinos and win with 100% guarantee. But many of these systems can really make you ... well... a little bit luckier. So do not look for the special system and just enjoy the game and may be some day you will be lucky enough to win a lot of money.