Pseudo-Random Numbers in C

  srand( seed); // initialize rand()

  r = rand();   // generate pseudo-random integer from 0 to RAND_MAX

  time(0) is current time in seconds since 1970

  double d; int r, seed = time(0);

  srand(seed); // just once, at beginning of main

  r = rand(); // 0 ≤ r ≤ RAND_MAX

  r = rand() % (b-a+1) + a; // range of int, a ≤ r ≤ b

  d = (rand()/(double)RAND_MAX)*(b-a) + a; // range of double, a ≤ d ≤ b

  The following functions define a portable implementation of rand() and srand():

  static unsigned long int next = 1;

  int rand(void) // RAND_MAX assumed to be 32767
  {
    next = next * 1103515245 + 12345;
    return (unsigned int)(next/65536) % 32768;
  }

  void srand(unsigned int seed)
  {
    next = seed;
  }