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copied!<p><code>srand()</code> seeds the random number generator. Without a seed, the generator is unable to generate the numbers you are looking for. As long as one's need for random numbers is not security-critical (e.g. any sort of cryptography), common practice is to use the system time as a seed by using the <code>time()</code> function from the <code><ctime></code> library as such: <code>srand(time(0))</code>. This will seed the random number generator with the system time expressed as a Unix timestamp (i.e. the number of seconds since the date 1/1/1970). You can then use <code>rand()</code> to generate a pseudo-random number.</p> <p>Here is a quote from a <a href="https://stackoverflow.com/questions/9459035/c-rand-gives-same-number-when-running-process">duplicate question</a>:</p> <blockquote> <p>The reason is that a random number generated from the rand() function isn't actually random. It simply is a transformation. Wikipedia gives a better explanation of the meaning of pseudorandom number generator: deterministic random bit generator. Every time you call rand() it takes the seed and/or the last random number(s) generated (the C standard doesn't specify the algorithm used, though C++11 has facilities for specifying some popular algorithms), runs a mathematical operation on those numbers, and returns the result. So if the seed state is the same each time (as it is if you don't call srand with a truly random number), then you will always get the same 'random' numbers out.</p> <p>If you want to know more, you can read the following:</p> <p><a href="http://www.dreamincode.net/forums/topic/24225-random-number-generation-102/" rel="nofollow noreferrer">http://www.dreamincode.net/forums/topic/24225-random-number-generation-102/</a></p> <p><a href="http://www.dreamincode.net/forums/topic/29294-making-pseudo-random-number-generators-more-random/" rel="nofollow noreferrer">http://www.dreamincode.net/forums/topic/29294-making-pseudo-random-number-generators-more-random/</a></p> </blockquote>

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