source code

/* immigration-emigration simulation */
#include        <stdio.h>
#include        <stdlib.h>

#define MAXTIME         100
#define PRNT_INTVL        10

int main(void)
{
  int    ttt, popSizeIncrement, popSize, seed;
  double alpha, beta;

  alpha = 0.1;
  beta = 0.1;
  popSize = 10;

  seed = 456739853;
  srand48(seed);

  printf("time\tpopSize\n");
  for (ttt = 0; ttt < MAXTIME; ttt++)
    {
      popSizeIncrement = 0;

      if(drand48() < alpha) popSizeIncrement = 1;
      if(drand48() < beta) popSizeIncrement = popSizeIncrement - 1;

      popSize += popSizeIncrement;
      if(popSize < 0) popSize = 0;

      if(ttt % PRNT_INTVL == 0) printf("%4d\t%-4d\n", ttt, popSize);
    }

  return(0);
}