```/* nag_bessel_i_alpha (s18ejc) Example Program.
*
* NAGPRODCODE Version.
*
* Copyright 2016 Numerical Algorithms Group.
*
* NAG C Library
*
* Mark 26, 2016.
*/

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

int main(void)
{
Complex *b = 0;
Integer exit_status = 0, i, nl;
NagError fail;
double a, alpha, d, x;

INIT_FAIL(fail);

/* Skip heading in data file */
scanf("%*[^\n]");
printf("nag_bessel_i_alpha (s18ejc) Example Program Results\n");
if (!(b = NAG_ALLOC(101, Complex)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
while (scanf("%lf %lf %" NAG_IFMT "%*[^\n]", &x, &a, &nl) != EOF)
{
printf("  x     a      nl\n");
printf("%4.1f  %4.1f %6" NAG_IFMT "\n\n", x, a, nl);
/* nag_bessel_i_alpha (s18ejc).
* Modified Bessel functions I_(alpha+n-1)(x) or
* I_(alpha-n+1)(x) for real x != 0, non-negative
* alpha < 1 and n = 1,2,...,|N|+1
*/
nag_bessel_i_alpha(x, a, nl, b, &fail);
if (fail.code == NE_NOERROR) {
printf(" Requested values of I_alpha(X)\n\n");
alpha = a;
printf("     alpha              I_alpha(X)\n");
for (i = 1; i <= ABS(nl) + 1; ++i) {
printf("%13.4e   (%13.4e, %13.4e)\n",
alpha, b[i - 1].re, b[i - 1].im);
d = (double) nl;
alpha += SIGN(1.0, d);
}
}
else {
printf("Error from nag_bessel_i_alpha (s18ejc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
}
END:
NAG_FREE(b);
return exit_status;
} /* main */
```