Code

 Header...
// Demonstrate a growable array 

# define GROWBY 4
// Growable array of floats
typedef struct floatarray {
  float *values;
  int nvals;
  int buflen;
}Floatarray;

// Allocate a new growable array
 Floatarray* newfloatarray(void){
   ... 

»  Floatarray *f;

»  f=xmalloc(sizeof *f);// NB xmalloc checks for NULL
»  f->buflen=f->nvals=0;
»  f->values=NULL;

»  return f;
}

// Add a value to an array, extending it if necessary
 void addtoarray(Floatarray *f,float value){
   ... 

  // Check to see if we need to extend the array
»  if (f->nvals==f->buflen) {
»    f->buflen+=GROWBY;
»    f->values=realloc(f->values, f->buflen*sizeof f->values);
  }
»  f->values(f->nvals)=value;
»  f->nvals++;
}

 int main(){
   ... 

»  Floatarray *far;
»  float value;

»  far=newfloatarray();

»  printf("Just keep typing in numbers!\n");

»  while (scanf("%g", &value)==1) {
»    addtoarray(far, value);
  }

»  printf("The array has %d elements\n", far->nvals);
»  for ( int i=0;i<far->nvals; ++i) 
    printf("%d: %g\n", i, far->values[i]);
  
»  return 0;
}