```/* nag_tsa_auto_corr (g13abc) Example Program.
*
* Copyright 2014 Numerical Algorithms Group.
*
* Mark 2, 1991.
* Mark 8 revised, 2004.
*
*/

#include <nag.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <nagg13.h>

int main(void)
{

Integer  exit_status = 0, i, nk, nx;
NagError fail;
double   mean, *r = 0, stat, *x = 0, xv;

INIT_FAIL(fail);

printf("nag_tsa_auto_corr (g13abc) Example Program Results\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%ld %ld", &nx, &nk);

if (nk > 0 && nx > 1 && nk < nx)
{
if (!(r = NAG_ALLOC(nk, double)) ||
!(x = NAG_ALLOC(nx, double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
}
else
{
printf("Invalid nx or nk.\n");
exit_status = 1;
return exit_status;
}
for (i = 0; i < nx; ++i)
scanf("%lf", &x[i]);
printf("\nThe first %2ld coefficients are required\n", nk);

/* nag_tsa_auto_corr (g13abc).
* Sample autocorrelation function
*/
nag_tsa_auto_corr(x, nx, nk, &mean, &xv, r, &stat, &fail);
if (fail.code != NE_NOERROR)
{
printf("Error from nag_tsa_auto_corr (g13abc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

printf("The input array has sample mean %12.4f\n", mean);
printf("The input array has sample variance %12.4f\n", xv);
printf("The sample autocorrelation coefficients are\n\n");
printf("   Lag    Coeff\n");
for (i = 0; i < 10; ++i)
printf("%6ld%10.4f\n", i+1, r[i]);
printf("\nThe value of stat is %12.4f\n", stat);
END:
NAG_FREE(r);
NAG_FREE(x);
return exit_status;
}
```