How does a computer calculate a 'random' number?

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Had an argument about computers and random numbers.
I said that pcs cannot make up random numbers, i was then 'proved wrong' ( ) by someone making a short program that outputted a 'random' number.

Randomness requires creativity (intelligence) which computers do not have. So i assume they have some hugely complicated formula to calculate a random number. Does anybody know how its done?

 

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random numbers do work
i made a application that does exactly that

NO! A computer cannot make a random number!
Functions available in programming, like "rand()" are good at simulating random numbers, but its not truely random.

The only way i can think of getting a true random number from a computer would be something like reading tiny variances in its power supply or variances in cpu temp (things which are influenced by our analogue world rather than made by the digial computer)

 

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haha, i'v explained this so many times today.

A computer can only do one thing: follow instructions.
You must tell it how to make the number, therefor its not a random number :/