Re: rand and srand

Bill Cunningham wrote:
The function rand() returns a value between 0 and RAND_MAX, not between
0 and what you pass to srand(). The latter function only sets the seed for the random number generator (on which the next random number will be based).

If you want to have a non-predictable sequence of random numbers, it's often a good idea to set the seed to something that is not a literal and will change each time the program is executed.

Additionally, if you want to generate a random number between 0 and 2000, the code to do that uses the modulus operator, thusly:

printf("%u\n", (rand() % 2001));

For one, without the \n (newline), nothing will separate your numbers from each other. The second part of this is the % 2001. That divides the value from rand() by 2001, and returns the remainder - so the number can be anything from 0 to 2000. If rand() returns 2001, the modulus makes it 0, etc.

Thanks so much for your advice. I haven't used code with modulus yet and this is the first time I've seen it.

As for your main(), I wasn't actually aware that such code was legal C. My guess is that it is actually void main(), because you never return a value from it, so the exit status of your program is most likely undefined. It is a good idea, particularly in UNIX, to declare it int, and return 0 at the end (unless the program failed).

The C99 standard wants and int. But all the compilers I've used accept main() and main(int argc,char *argv[]) when parameters are used. Otherwise automatic void of course with just () as parameters. Thanks for the advice on rand. So is there really a need to use srand ( ) ?

Bill



The function srand() sets the seed for the algorithm that returns the next random number. It is highly recommended that you set it to something or another, particularly (part of) the system time. If you don't, the sequence will be static and not really that random at all.

--
--Falcon Kirtaran
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