1  #include <math.h>
       2  #include <stdio.h>
       3  
       4  extern double a;
       5  
       6  int main ()
       7  {
       8    if (! isfinite (a))
       9      printf ("infinity detected\n");
      10  
      11    a = 1.0/1.0;
      12  
      13    if (isfinite (a))
      14      printf ("number is now finite\n");
      15    return 0;
      16  }