```/* nag_1d_spline_interpolant (e01bac) Example Program.
*
* Copyright 2014 Numerical Algorithms Group.
*
* Mark 2, 1991.
*
* Mark 6 revised, 2000.
* Mark 8 revised, 2004.
*/

#include <nag.h>
#include <stdio.h>
#include <math.h>
#include <nag_stdlib.h>
#include <nage01.h>
#include <nage02.h>

#define MMAX 7

int main(void)
{
Integer    exit_status = 0, i, j, m = MMAX;
NagError   fail;
Nag_Spline spline;
double     fit, *x = 0, xarg, *y = 0;

INIT_FAIL(fail);

/* Initialise spline */
spline.lamda = 0;
spline.c = 0;

printf(
"nag_1d_spline_interpolant (e01bac) Example Program Results\n");

if (m >= 1)
{
if (!(y = NAG_ALLOC(m, double)) ||
!(x = NAG_ALLOC(m, double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
}
else
{
exit_status = 1;
return exit_status;
}

x[0] = 0.0; x[1] = 0.2; x[2] = 0.4;
x[3] = 0.6; x[4] = 0.75; x[5] = 0.9; x[6] = 1.0;

for (i = 0; i < m; ++i)
y[i] = exp(x[i]);
/* nag_1d_spline_interpolant (e01bac).
* Interpolating function, cubic spline interpolant, one
* variable
*/
nag_1d_spline_interpolant(m, x, y, &spline, &fail);
if (fail.code != NE_NOERROR)
{
printf("Error from nag_1d_spline_interpolant (e01bac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

printf("\nNumber of distinct knots = %ld\n\n", m-2);
printf("Distinct knots located at \n\n");
for (j = 3; j < m+1; j++)
printf("%8.4f%s", spline.lamda[j], (j-3)%5 == 4 || j == m?"\n":" ");
printf("\n\n    J    B-spline coeff c\n\n");
for (j = 0;  j < m; ++j)
printf("    %ld  %13.4f\n", j+1, spline.c[j]);
printf(
"\n    J       Abscissa            Ordinate            Spline\n\n");
for (j = 0; j < m; ++j)
{
/* nag_1d_spline_evaluate (e02bbc).
* Evaluation of fitted cubic spline, function only
*/
nag_1d_spline_evaluate(x[j], &fit, &spline, &fail);
if (fail.code != NE_NOERROR)
{
printf("Error from nag_1d_spline_evaluate (e02bbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

printf("    %ld %13.4f      %13.4f       %13.4f\n",
j+1, x[j], y[j], fit);
if (j < m-1)
{
xarg = (x[j] + x[j+1]) * 0.5;
/* nag_1d_spline_evaluate (e02bbc), see above. */
nag_1d_spline_evaluate(xarg, &fit, &spline, &fail);
if (fail.code != NE_NOERROR)
{
printf(
"Error from nag_1d_spline_evaluate (e02bbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
printf("      %13.4f                          %13.4f\n",
xarg, fit);
}
}
/* Free memory allocated by nag_1d_spline_interpolant (e01bac) */
END:
NAG_FREE(y);
NAG_FREE(x);
NAG_FREE(spline.lamda);
NAG_FREE(spline.c);
return exit_status;
}
```