```/* nag_1d_quad_brkpts_1 (d01slc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.1, 2017.
*
*/

#include <nag.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <math.h>
#include <nagd01.h>

#ifdef __cplusplus
extern "C"
{
#endif
static double NAG_CALL f(double x, Nag_User *comm);
#ifdef __cplusplus
}
#endif

int main(void)
{
static Integer use_comm = { 1 };
Integer exit_status = 0;
double a, b;
double epsabs, abserr, epsrel, brkpts, result;
Integer nbrkpts;
Integer max_num_subint;
NagError fail;
Nag_User comm;

INIT_FAIL(fail);

/* For communication with user-supplied functions: */
comm.p = (Pointer) &use_comm;

nbrkpts = 1;
epsabs = 0.0;
epsrel = 0.001;
a = 0.0;
b = 1.0;
max_num_subint = 200;
brkpts = 1.0 / 7.0;
* singularities at specified points, thread-safe
*/
nag_1d_quad_brkpts_1(f, a, b, nbrkpts, brkpts, epsabs, epsrel,
max_num_subint, &result, &abserr, &qp, &comm, &fail);
printf("a      - lower limit of integration = %10.4f\n", a);
printf("b      - upper limit of integration = %10.4f\n", b);
printf("epsabs - absolute accuracy requested = %11.2e\n", epsabs);
printf("epsrel - relative accuracy requested = %11.2e\n\n", epsrel);
printf("brkpts - given break-point = %10.4f\n", brkpts);
if (fail.code != NE_NOERROR)
printf("Error from nag_1d_quad_brkpts_1 (d01slc) %s\n", fail.message);
if (fail.code != NE_INT_ARG_LT && fail.code != NE_2_INT_ARG_LE &&
fail.code != NE_ALLOC_FAIL && fail.code != NE_NO_LICENCE) {
/* Free memory used by qp */
NAG_FREE(qp.sub_int_beg_pts);
NAG_FREE(qp.sub_int_end_pts);
NAG_FREE(qp.sub_int_result);
NAG_FREE(qp.sub_int_error);
}
if (fail.code != NE_INT_ARG_LT && fail.code != NE_2_INT_ARG_LE
&& fail.code != NE_QUAD_BRKPTS_INVAL && fail.code != NE_ALLOC_FAIL
&& fail.code != NE_NO_LICENCE) {
printf("result - approximation to the integral = %9.5f\n", result);
printf("abserr - estimate of the absolute error = %11.2e\n", abserr);
printf("qp.fun_count  - number of function evaluations = %4" NAG_IFMT
"\n", qp.fun_count);
printf("qp.num_subint  - number of subintervals used = %4" NAG_IFMT "\n",
qp.num_subint);
}
else {
exit_status = 1;
goto END;
}

END:
return exit_status;
}

static double NAG_CALL f(double x, Nag_User *comm)
{
double a;
Integer *use_comm = (Integer *) comm->p;

if (use_comm) {
printf("(User-supplied callback f, first invocation.)\n");
use_comm = 0;
}

a = FABS(x - 1.0 / 7.0);
return (a != 0.0) ? pow(a, -0.5) : 0.0;
}
```