NAG Library Manual, Mark 27.2
```/* D01UA_T1W_F C++ Header Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
* Mark 27.2, 2021.
*/

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

extern "C"
{
static void NAG_CALL f_t1w(void *&                 ad_handle,
const Integer &         nx,
Integer &               iflag,
Integer                 iuser[],
}

int main(void)
{
// Scalars
int     exit_status = 0;
Integer n           = 64;
// Arrays
Integer           iuser[1];

ruser[0] = 1.0;

cout << "D01UA_T1W_F C++ Header Example Program Results\n\n";

cout << "\n Derivatives calculated: First order tangents\n";
cout << " Computational mode    : algorithmic\n";

// Create AD configuration Data object
Integer ifail     = 0;

Integer           key;
for (int funid = 1; funid <= 6; funid++)
{
if (funid == 1)
{
a   = 0.0;
b   = 1.0;
key = 0;
}
if (funid == 2)
{
a   = 2.0;
b   = 0.0;
key = -5;
}
if (funid == 3)
{
a   = 2.0;
b   = 1.0;
key = -3;
}
if (funid == 4)
{
a   = 2.0;
b   = 1.0;
key = 3;
}
if (funid == 5)
{
a   = -1.0;
b   = 3.0;
key = -4;
}
if (funid == 6)
{
a   = -1.0;
b   = 3.0;
key = 4;
}

iuser[0] = funid;

ifail = 0;
double            inc = 1.0, zero = 0.0;
dco::derivative(ruser[0]) = inc;
ruser, ifail);
dco::derivative(ruser[0]) = zero;

// Get derivatives
double dr;
dr = dco::derivative(dinest);

cout.setf(ios::scientific, ios::floatfield);
cout.setf(ios::right);
cout.precision(4);
cout << "\n dinest = ";
double dinest_value = dco::value(dinest);
cout.width(12);
cout << dinest_value << "     ";
cout << " d/druser[0] = ";
cout.width(12);
cout << dr << endl;
}

// Remove computational data object

return exit_status;
}

static void NAG_CALL f_t1w(void *&                 ad_handle,
const Integer &         nx,
Integer &               iflag,
Integer                 iuser[],
{
Integer           i;
for (i = 0; i < nx && iflag >= 0; i++)
{
xx  = x[i];
rux = ruser[0] * xx;
if (iuser[0] == 1)
{
fx = 4.0 / (1.0 + ruser[0] * xx * xx);
}
if (iuser[0] == 2)
{
fx = 1.0 / (xx * xx * log(ruser[0] * xx));
}
if (iuser[0] == 3)
{
fx = exp(-ruser[0] * xx) / xx;
}
if (iuser[0] == 4)
{
fx = ruser[0] / xx;
}
if (iuser[0] == 5)
{
fx = exp(-3.0 * ruser[0] * xx * xx - 4.0 * xx - 1.0);
}
if (iuser[0] == 6)
{
fx = exp(2.0 * ruser[0] * xx + 2.0);
}
if (iuser[0] < 0 || iuser[0] > 6)
{
iflag = -1;
}
fv[i] = fx;
}

return;
}
```