```/* C05QC_T1W_F C++ Header Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
* Mark 27, 2019.
*/

#include <nag.h>
#include <dco.hpp>
#include <stdio.h>
#include <math.h>
#include <nagx02.h>
#include <nagx04.h>
#include <iostream>
#include <string>
using namespace std;

extern "C"
{
const Integer &n,
Integer iuser[],
Integer &iflag);
}

int main (void)
{
// Scalars
int               exit_status = 0;
const Integer     maxfev = 2000, ml = 1, mode = 2,
mu = 1, n = 7, nprint = 0;

cout << "C05QC_T1W_F C++ Header Example Program Results\n\n";

// problem parameters and starting value

ruser[0] = -1.0;
ruser[1] =  3.0;
ruser[2] = -2.0;
ruser[3] = -2.0;
ruser[4] = -1.0;

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

nagad_t1w_w_rtype diag[n], fjac[n*n], epsfcn, factor, fvec[n],
qtf[n], r[n*(n+1)/2], xtol;
double dr[5*n];
Integer           iuser[1], nfev;

xtol = sqrt(X02AJC);
epsfcn = 0.;
factor = 100.;

for (int i=0; i<5; ++i) {
for (int j=0; j<n; ++j) {
x[j] = -1.0;
diag[j] = 1.;
}

dco::derivative(ruser[i]) = 0.5;

ifail = 0;
diag,factor,nprint,nfev,fjac,r,qtf,iuser,ruser,ifail);

for (int j=0; j<n; ++j) {
dr[i*n + j] = 2.*dco::derivative(x[j]);
}

dco::derivative(ruser[i]) = 0.;
}

cout.setf(ios::scientific,ios::floatfield);
cout.precision(4);
cout << "           Solution:\n";
for (int i=0; i<n; ++i) {
cout.width(10);
cout << i+1;
cout.width(20);
cout << dco::value(x[i]) << endl;
}

cout << "\n Derivatives calculated: First order tangents\n";
cout << " Computational mode    : algorithmic\n";
cout << "\n Derivatives are of solution w.r.t function params\n\n";

NagError  fail;
INIT_FAIL(fail);
x04cac(Nag_ColMajor,Nag_GeneralMatrix,Nag_NonUnitDiag,n,5,dr,n,
"    dx/druser",0,&fail);

// Remove computational data object

return exit_status;
}

const Integer &n,
Integer iuser[],
Integer &iflag)
{
if (iflag!=0) {
for (int i=0; i<n; ++i) {
fvec[i] = (ruser[1] + ruser[2]*x[i])*x[i] - ruser[4];
}
for (int i=1; i<n; ++i) {
fvec[i] = fvec[i] + ruser[0]*x[i-1];
}
for (int i=0; i<n-1; ++i) {
fvec[i] = fvec[i] + ruser[3]*x[i+1];
}
}
iflag = 0;
return;
}
```