```/* nag_interp_dim1_everett (e01abc) Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
*
* Mark 27.0, 2019.
*/

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

int main(void)
{
/* Scalars */
Integer exit_status = 0;
Integer i, n, r;
double p;

/* Local Arrays */
double *a = 0, *g = 0;

/* Nag Types */
NagError fail;

INIT_FAIL(fail);

printf("nag_interp_dim1_everett (e01abc) Example Program Results\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%" NAG_IFMT "", &n);
scanf("%lf", &p);
scanf("%*[^\n] ");

/* Allocate memory */
if (!(a = NAG_ALLOC((2 * n), double)) ||
!(g = NAG_ALLOC((2 * n + 1), double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

for (i = 0; i < 2 * n; i++)
scanf("%lf", &a[i]);
scanf("%*[^\n] ");

/* nag_interp_dim1_everett (e01abc).
* Interpolated values, Everett's formula, equally spaced data, one variable.
*/
nag_interp_dim1_everett(n, p, a, g, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_interp_dim1_everett (e01abc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

printf("\n");
for (r = 0; r <= n - 1; r++) {
printf("Central differences order %" NAG_IFMT "  of Y0 = %12.5f\n",
r, g[2 * r]);
printf("                                Y1 = %12.5f\n", g[2 * r + 1]);
}
printf("\n");
printf("Function value at interpolation point = %12.5f\n", g[2 * n]);

END:
NAG_FREE(a);
NAG_FREE(g);

return exit_status;
}
```