I'm making a game in c++ and it involves filling tiles with random booleans (either yes or no) whether it is yes or no is decided by rand() % 1. It doesnt feel very random. I'm using srand with ctime at startup, but it seems like the same patterns are coming up. Are there any algorithms that will create very random numbers? Or any suggestions on how I could improve rand()?
Thanks
The perfect way of Yes or No as random is toggling those. You may not need random function.
The lowest bits of standard random number generators aren't very random, this is a well known problem.
I'd look into the boost random number library.
True randomness often doesn't seem very random. Do expect to see odd runs.
But at least one immediate thing you can do to help is to avoid using just the lowest-order bit. To quote Numerical Recipes in C:
If you want to generate a random integer between 1 and 10, you should always do it by using high-order bits, as in
j = 1 + (int) (10.0 * (rand() / (RAND_MAX + 1.0)));
and never by anything resembling
j = 1 + (rand() % 10);
(which uses lower-order bits).
Also, you might consider using a different RNG with better properties instead. The Xorshift algorithm is a nice alternative. It's speedy and compact at just a few lines of C, and should be good enough statistically for nearly any game.
Many pseudo-random number generators suffer from cyclical lower bits, especially linear congruential algorithms, which are typically the most common implementations. Some people suggest shifting out the least significant bits to solve this.
Also if you reseed too fast then you will get the exact same number. Personally I use a class that updates the seed only when the time has changed.
A quick thing that might make your numbers feel a bit more random would be to re-seed the generator each time the condition if(rand() % 50==0) is true.
The low order bits are not very random.
By using %2 you are only checking the bottom bit of the random number.
Assuming you are not needing crypto strength randomness.
Then the following should be OK.
bool tile = rand() > (RAND_MAX / 2);
People say lower-order bits are not random. So try something from the middle. This will get you the 28th bit:
(rand() >> 13) % 2
Knuth suggests a Random number generation by subtractive method. Its is believed to be quite randome. For a sample implementation in the Scheme language see here
I have used the Mersenne Twister random number generator successfully for many years. Its source code is available from the maths department of Hiroshima Uni here. (Direct link so you don't have to read Japanese!)
What is great about this algorithm is that:
I'd recommend giving it a look for your game.
With random numbers to get good results you really need to have a generator that combines several generators's results. Just discarding the bottom bit is a pretty silly answer.
multiply with carry is simple to implement and has good results on its own and if you have several of them and combine the results you will get extremely good results. It also doesn't require much memory and is very fast.