Why ’42’ is the preferred number when indicating something random

Random Number Generators(RNGs) are really generating pseudorandom numbers, since it's impossible to actually generate a TRULY random number. The only really truly random things are acts of God, like lightning.

This wikipedia article might be able to help you out in the explanation: http://en.wikipedia.org/wiki/Random_number_generators

From what I understand, there are basically two parts of an RNG: the seed, and then the random number chosen from that seed. When you seed the RNG, you are giving it an equivalent to a starting point. That starting point then has a bunch of numbers that are "inside" of it that the program chooses from. In PHP, you can use srand() to "shuffle" the seeds, so you almost always get a different answer. You can then use rand(min, max) to go into the seed and choose a number between the min and the max, inclusive.

WARNING, POSSIBLE CHEESY ANALOGY AHEAD!

Think of each 'seed' as an ice chest, and then the random numbers as ice cubes. Let's say you have 1000 ice chests and each chest has 1000 ice cubes inside. At the county fair, they'll choose an ice chest to start using for drinks, and they can only use one ice cube. However, they only need ice cubes bigger than 1 cubic inch. So they'll choose a chest at random between those 1000 chests, and then they'll choose an ice cube inside that chest at random. If it works for the size they want, they use it. If it's not, they put it back in the chest with the others. If they want to make it a little more fun they change chests beforehand for total obliviousness, if you will!

As for how PHP actually physically chooses the seed and the random number, I don't have enough knowledge for that(which is probably what you were wondering the most about!). I wouldn't try and redo the rand() function; for most web based applications that you'll make, rand() should suffice for any random number you'll need.

Also check out linear congruential generators, this might be more of what you're looking for if you want the dirty details: http://en.wikipedia.org/wiki/Linear_congruential_generator

Hope this helps!

The number is treated as an unsigned integer in this case which means all bits set will not produce -1 (if it were signed then yes, you would be correct). So all 16 bits set will give you 65535.

Interestingly enough though, signed state isn't a factor when doing logic bit-operations. Bits are themselves not signed as they are the lowest component in a computer. It's specified by the cpu operation if the bits in ex. a register will be treated signed or unsigned.

Negative numbers are produced by setting the most significant bit (MSB) to true IF the number is treated as signed (which "side", or which outer bit will be set varies depending on cpu architecture, ie. big-endian / little-endian) .