NAG Library Manual, Mark 28.4
```/* nag_zeros_cubic_real (c02akc) Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
*
* NAG C Library
*
* Mark 28.4, 2022.
*/

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

int main(void) {
double *errest = 0, *zeroi = 0, *zeror = 0;
double r, s, t, u;
Integer i;
Integer exit_status = 0;
NagError fail;

INIT_FAIL(fail);

printf("nag_zeros_cubic_real (c02akc) Example Program Results\n\n");

if (!(errest = NAG_ALLOC(3, double)) || !(zeroi = NAG_ALLOC(3, double)) ||
!(zeror = NAG_ALLOC(3, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%lf %lf %lf %lf ", &u, &r, &s, &t);

/* nag_zeros_cubic_real (c02akc).
* Zeros of a cubic polynomial with real coefficients
*/
nag_zeros_cubic_real(u, r, s, t, zeror, zeroi, errest, &fail);
if (fail.code == NE_NOERROR) {
printf("\n Roots of cubic equation             Error estimates\n");
printf("                                   (machine-dependent)\n\n");
for (i = 0; i <= 2; ++i) {
printf(" z = %10.5f %10.5f%s         %g\n", zeror[i], zeroi[i], "*i",
errest[i]);
}
} else {
printf("Error from nag_zeros_cubic_real (c02akc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

END:
NAG_FREE(errest);
NAG_FREE(zeroi);
NAG_FREE(zeror);
return exit_status;
}
```