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Showing content from https://cplusplus.com/reference/cstdlib/srand/ below:

function

<cstdlib>

void srand (unsigned int seed);

Initialize random number generator

For every different seed value used in a call to srand, the pseudo-random number generator can be expected to generate a different succession of results in the subsequent calls to rand.

Two different initializations with the same seed will generate the same succession of results in subsequent calls to rand.

If seed is set to 1, the generator is reinitialized to its initial value and produces the same values as before any call to rand or srand.

In order to generate random-like numbers, srand is usually initialized to some distinctive runtime value, like the value returned by function time (declared in header <ctime>). This is distinctive enough for most trivial randomization needs.

seed

An integer value to be used as seed by the pseudo-random number generator algorithm.

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/* srand example */
#include <stdio.h>      /* printf, NULL */
#include <stdlib.h>     /* srand, rand */
#include <time.h>       /* time */

int main ()
{
  printf ("First number: %d\n", rand()%100);
  srand (time(NULL));
  printf ("Random number: %d\n", rand()%100);
  srand (1);
  printf ("Again the first number: %d\n", rand()%100);

  return 0;
}

First number: 41
Random number: 13
Again the first number: 41

Some libraries provide an alternative function of rand that explicitly avoids this kind of data race: rand_r (non-portable).

C++ library implementations are allowed to guarantee no data races for calling this function.

rand

Generate random number (function)

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