```/* D01RL_P0W_F C++ Header Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
* Mark 27, 2019.
*/

#include <nag.h>
#include <stdio.h>
#include <math.h>
#include <iostream>
using namespace std;

extern "C"
{
static void NAG_CALL f(void * &ad_handle,
const double x[],
const Integer &nx,
double fv[],
Integer &iflag,
Integer iuser[],
double ruser[],
const void *&cpuser);
}

int main(void)
{
// Scalars
int               exit_status = 0;

cout << "D01RL_P0W_F C++ Header Example Program Results\n\n";

double a, b, epsabs, epsrel;
a = 0.0;
b = 1.0;
epsabs = 0.0;
epsrel = 1.0e-4;

Integer npts   = 1;
Integer maxsub = 20;
Integer lrinfo = 80 + npts + 6;
Integer liinfo = 40 + npts + 4;
double  *rinfo = 0;
Integer *iinfo = 0;

rinfo = new double [lrinfo];
iinfo = new Integer [liinfo];

double  result, abserr, ruser[20], points[1];
Integer iuser[1];
const void *cpuser = 0;
points[0] = 1.0/7.0;
iuser[0] = 0;
for (int i = 0; i<20; ++i) {
ruser[i] = 0.0;
}

// Call the passive routine

Integer ifail = -1;
rinfo,iinfo,iuser,ruser,cpuser,ifail);
if (ifail<0) {
cout << "\n ** d01rl_p0w_f_ failed error exit ifail = " << ifail << endl;
goto END;
}
// Print inputs and primal outputs.
cout << "\n lower limit of integration (a) = " << a << endl;
cout << " upper limit of integration (b) = " << b << endl;
cout << " given break point (points[0])  = " << points[0] << endl;
cout << " absolute accuracy requested    = " << epsabs << endl;
cout << " relative accuracy requested    = " << epsrel << endl;
cout << " maximum number of subintervals = " << maxsub << endl;
cout.setf(ios::scientific,ios::floatfield);
cout.precision(4);
if (ifail >= 0) {
cout << "\n approximation to the integral  : " << result << endl;
cout << " estimate of the absolute error : " << abserr << endl;
cout << " number of function evaluations : " << iinfo[0] << endl;
}

END:

delete [] rinfo;
delete [] iinfo;
return exit_status;
}

static void NAG_CALL f(void * &ad_handle,
const double x[],
const Integer &nx,
double fv[],
Integer &iflag,
Integer iuser[],
double ruser[],
const void *&cpuser)
{
iflag = 0;
for (int i=0; i<nx; i++) {
fv[i] = x[i] - 1.0/7.0;
if (fv[i] == 0.0) {
ruser[iflag] = x[i];
iflag++;
} else if (fv[i] < 0.0) {
fv[i] = -fv[i];
}
}
iuser[0] = iflag;
if (iflag == 0) {
for (int i=0; i<nx; i++) {
fv[i] = 1.0/sqrt(fv[i]);
}
} else {
iflag = -iflag;
}
return;
}
```