```/* nag_dsum (f16elc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.1, 2017.
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nagf16.h>

int main(void)
{
/* Scalars */
Integer exit_status, i, incx, ix, n;
double sumval;
/* Arrays */
double *x = 0;
/* Nag Types */
NagError fail;

exit_status = 0;
INIT_FAIL(fail);

printf("nag_dsum (f16elc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
/* Read the number of elements and the increment */
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &n, &incx);

if (n > 0) {
/* Allocate memory */
if (!(x = NAG_ALLOC(MAX(1, 1 + (n - 1) * ABS(incx)), double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
}
else {
printf("Invalid n\n");
exit_status = 1;
goto END;
}

/* Read the vector x and store forwards or backwards
* as determined by incx. */
for (i = 0, ix = (incx > 0 ? 0 : (1-n)*incx); i < n; i++, ix += incx)
scanf("%lf", &x[ix]);
scanf("%*[^\n] ");

/* nag_dsum (f16elc).
* Sum elements of a vector of doubles */
sumval = nag_dsum(n, x, incx, &fail);

if (fail.code != NE_NOERROR) {
printf("Error from nag_dsum (f16elc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print the result. */
printf("Sum of elements of x is %9.5f\n", sumval);

END:
NAG_FREE(x);

return exit_status;
}
```