```/* nag_bessel_k0_vector (s18aqc) Example Program.
*
* Copyright 2014 Numerical Algorithms Group.
*
* Mark 23, 2011.
*/
#include <nag.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <nags.h>

int main(void)
{
Integer  exit_status = 0;
Integer  i, n;
double   *f = 0, *x = 0;
Integer  *ivalid = 0;
NagError fail;

INIT_FAIL(fail);

/* Skip heading in data file */
scanf("%*[^\n]");

printf("nag_bessel_k0_vector (s18aqc) Example Program Results\n");
printf("\n");
printf("     x           f          ivalid\n");
printf("\n");
scanf("%ld", &n);
scanf("%*[^\n]");

/* Allocate memory */
if (!(x = NAG_ALLOC(n, double)) ||
!(f = NAG_ALLOC(n, double)) ||
!(ivalid = NAG_ALLOC(n, Integer)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

for (i=0; i<n; i++)
scanf("%lf", &x[i]);
scanf("%*[^\n]");

/* nag_bessel_k0_vector (s18aqc).
* modified Bessel Function K0(x)
*/
nag_bessel_k0_vector(n, x, f, ivalid, &fail);
if (fail.code!=NE_NOERROR && fail.code!=NW_IVALID)
{
printf("Error from nag_bessel_k0_vector (s18aqc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

for (i=0; i<n; i++)
printf(" %11.3e %11.3e %4ld\n", x[i], f[i], ivalid[i]);

END:
NAG_FREE(f);
NAG_FREE(x);
NAG_FREE(ivalid);

return exit_status;
}
```