```/* nag_fft_3d (c06pxc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.2, 2017.
*/

#include <nag.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <nagc06.h>
#include <nagx04.h>

static Integer writex(Integer n1, Integer n2, Integer n3, Complex *x)
{
/* Routine to print 3D matrix in 2D slices. */
Integer k;
NagError fail;

INIT_FAIL(fail);

for (k = 1; k <= n3; k++) {
char title[30];
sprintf(title, "X(i,j,k) for k = %" NAG_IFMT, k);
fflush(stdout);
nag_gen_complx_mat_print_comp(Nag_ColMajor, Nag_GeneralMatrix,
Nag_NonUnitDiag, n1, n2,
&x[(k - 1) * n1 * n2], n1, Nag_BracketForm,
"%6.3f", title, Nag_NoLabels, 0,
Nag_NoLabels, 0, 90, 0, 0, &fail);
printf("\n");
}
if (fail.code != NE_NOERROR) {
printf("Error from nag_gen_complx_mat_print_comp (x04dbc).\n%s\n",
fail.message);
return 1;
}
return 0;
}

int main(void)
{
/* Scalars */
Integer i, j, k, n1, n2, n3;
Integer exit_status = 0;
NagError fail;
/* Arrays */
Complex *x = 0;
#define X(I, J, K) x[(K-1)*n2*n1 + (J-1)*n1 + I - 1]

INIT_FAIL(fail);

printf("nag_fft_3d (c06pxc) Example Program Results\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "", &n1, &n2, &n3);
scanf("%*[^\n]");
if (n1 * n2 * n3 >= 1) {
/* Allocate memory */
if (!(x = NAG_ALLOC(n1 * n2 * n3, Complex)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* Read in complex data and print out. */
for (k = 1; k <= n3; ++k) {
for (i = 1; i <= n1; ++i) {
for (j = 1; j <= n2; ++j) {
scanf(" ( %lf, %lf ) ", &X(i, j, k).re, &X(i, j, k).im);
}
}
}
printf("\nOriginal data values\n\n");
exit_status = writex(n1, n2, n3, x);
if (exit_status != 0) {
goto END;
}
/* Compute transform */
/* nag_fft_3d (c06pxc).
* Three-dimensional complex discrete Fourier transform,
* complex data format
*/
nag_fft_3d(Nag_ForwardTransform, n1, n2, n3, x, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_fft_3d (c06pxc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

printf("\nComponents of discrete Fourier transforms\n\n");
exit_status = writex(n1, n2, n3, x);
if (exit_status != 0) {
goto END;
}
/* Compute inverse transform */
/* nag_fft_3d (c06pxc), see above. */
nag_fft_3d(Nag_BackwardTransform, n1, n2, n3, x, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_fft_3d (c06pxc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
printf("\nOriginal data as restored by inverse transform\n\n");
exit_status = writex(n1, n2, n3, x);
}
else
printf("\nInvalid value of n1, n2 or n3.\n");

END:
NAG_FREE(x);

return exit_status;
}
```