```/* nag_dtrttp (f01vac) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.1, 2017.
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nagf01.h>
#include <nagx04.h>

int main(void)
{
/* Scalars */
Integer exit_status = 0, indent = 0, ncols = 80, i, j, pda;
Integer lenap, n;
/* Arrays */
double *a = 0, *ap = 0;
char nag_enum_arg[40], form[] = "%5.2f";
/* Nag Types */
Nag_MatrixType matrix;
Nag_OrderType order;
Nag_UploType uplo;
NagError fail;

#ifdef NAG_COLUMN_MAJOR
#define A(I, J) a[J*pda + I]
order = Nag_ColMajor;
#define KU(I,J) (I + J*(J+1)/2)
#define KL(I,J) (J*(n-1) - J*(J-1)/2 + I)
#else
#define A(I, J) a[I*pda + J]
order = Nag_RowMajor;
#define KL(I,J) (J + I*(I+1)/2)
#define KU(I,J) (I*(n-1) - I*(I-1)/2 + J)
#endif

INIT_FAIL(fail);

printf("nag_dtrttp (f01vac) Example Program Results\n\n");
/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%" NAG_IFMT "%*[^\n] ", &n);
scanf("%39s  %*[^\n] ", nag_enum_arg);
pda = n;
lenap = (n * (n + 1)) / 2;
if (!(a = NAG_ALLOC(pda * n, double)) || !(ap = NAG_ALLOC(lenap, double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
uplo = (Nag_UploType) nag_enum_name_to_value(nag_enum_arg);
/* Read a triangular matrix of order n. */
for (i = 0; i < n; i++) {
if (uplo == Nag_Upper) {
for (j = i; j < n; j++)
scanf("%lf", &A(i, j));
scanf("%*[^\n] ");
}
else {
for (j = 0; j <= i; j++)
scanf("%lf", &A(i, j));
scanf("%*[^\n] ");
}
}

/* Print the unpacked matrix. */
matrix = (uplo == Nag_Upper ? Nag_UpperMatrix : Nag_LowerMatrix);

/* nag_gen_real_mat_print_comp (x04cbc).
* Print real general matrix (comprehensive).
*/
fflush(stdout);
nag_gen_real_mat_print_comp(order, matrix, Nag_NonUnitDiag, n, n, a, pda,
form, "Unpacked Matrix A:", Nag_IntegerLabels,
NULL, Nag_IntegerLabels, NULL, ncols, indent,
NULL, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_gen_real_mat_print_comp (x04cbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
printf("\n");

/* Convert to triangular matrix from full to packed vector form using
* nag_dtrttp (f01vac).
*/
nag_dtrttp(order, uplo, n, a, pda, ap, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_dtrttp (f01vac).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print the packed vector using macros KL or KU. */
printf(" Packed Array AP (printed using KL/KU macros):\n\n");
for (i = 0; i < n; i++) {
printf("  ");
if (uplo == Nag_Upper) {
for (j = 0; j < i; j++)
printf("%6s", " ");
for (j = i; j < n; j++)
printf("%6.2f", ap[KU(i, j)]);
}
else {
for (j = 0; j <= i; j++)
printf("%6.2f", ap[KL(i, j)]);
}
printf("\n");
}

END:
NAG_FREE(a);
NAG_FREE(ap);
return exit_status;
}
```