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Please help me to correct my mistakes.

spring2014 (60)
Dear Friends,
I wrote a code to get a number from 5 files and do calculations and write the output in other file. It works well. But Now I want to develop it to read 9numbers from each file one by one and do calculations and write the 9 outputs in a txt file. But it does not work. Would you please help me?
I mean
afile-ti: 3 5 7 9 11 13 ...

afile-xi: 0 0 1 0 1 01 ....

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//this code works well//
  #include <iostream>
#include <cmath>
#include <fstream>


using namespace std;

/* function prototypes */

double f1(double, double, double);
double f2(double, double, double);

double euler2m(double(*)(double, double, double),
               double(*)(double, double, double),
               double, double, double, double,
               double&, double&);

int main()
{
    double ti, xi, vi, tf, xf, vf, dt, tmax;


/* initial information */

    ifstream inputFile1("afile-ti.txt");
    ifstream inputFile2("afile-xi.txt");
    ifstream inputFile3("afile-vi.txt");
    ifstream inputFile4("afile-dt.txt");
    ifstream inputFile5("afile-tmax.txt");
    ofstream outputFile("output3.txt");
 /*
    ti = 0.0;             // initial value for variable
    xi = 0.0;             // initial value for function x(t)
    vi = 1.0;             // initial
    dt = 0.1;             // step size for integration
    tmax = 12.0;          // integrate from ti till tmax */

            inputFile1>>tf;
        	inputFile2>>xi;
        	inputFile3>>vi;
        	inputFile4>>dt;
        	inputFile5>>tmax;



/* integration of ODE */
    while (ti <= tmax)
    {
    	tf = ti + dt;
    	euler2m(f1,f2,ti,xi,vi,tf,xf,vf);
        ti = tf;
        xi = xf;
        vi = vf;
    }
        cout<<"t="<<tf<<"\t"<<"x="<<xf<<"\t"<<"x'="<<vf<<"\n";
        outputFile<<"t="<<tf<<"\t"<<"x="<<xf<<"\t"<<"x'="<<vf<<"\n";

    return 0;
}

/*
  Definition of the x'(t) = f1(t,x,x') = x' by the definition
*/
    double f1(double t, double x, double v)
{
    double d1x;
    d1x = v;
    return d1x;
}
/*
 *  Definition of the x"(t) = f2(t,x,x')
*/
    double f2(double t, double x, double v)
{
    double d2x;
    d2x = (t*t);
    return d2x;
}

//-----------------------------------------------------------------------

    double euler2m(double(*d1x)(double, double, double),
                   double(*d2x)(double, double, double),
                   double ti, double xi, double vi, double tf,
                   double& xf, double& vf)
    {
        xf = xi + d1x(ti,xi,vi)*(tf-ti);
        vf = vi + d2x(ti,xi,vi)*(tf-ti);
    /* correction */
        xf = xi + (d1x(ti,xi,vi)+d1x(ti,xf,vf))*0.5*(tf-ti);
        vf = vi + (d2x(ti,xi,vi)+d2x(ti,xf,vf))*0.5*(tf-ti);
       return 0.0;
    }

//this code does not work well//
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#include <iostream>
#include <cmath>
#include <fstream>


using namespace std;

/* function prototypes */

double f1(double, double, double);
double f2(double, double, double);

double euler2m(double(*)(double, double, double),
               double(*)(double, double, double),
               double, double, double, double,
               double&, double&);

int main()
{
    double ti[10], xi[10], vi[10], tf[10], xf[10], vf[10], dt[10], tmax[10];
    int i;

/* initial information */

    ifstream inputFile1("afile-ti.txt");
    ifstream inputFile2("afile-xi.txt");
    ifstream inputFile3("afile-vi.txt");
    ifstream inputFile4("afile-dt.txt");
    ifstream inputFile5("afile-tmax.txt");
    ofstream outputFile("output3.txt");
 /*
    ti = 0.0;             // initial value for variable
    xi = 0.0;             // initial value for function x(t)
    vi = 1.0;             // initial
    dt = 0.1;             // step size for integration
    tmax = 12.0;          // integrate from ti till tmax */


    for (i=0; i<=9; i++)
    {
            inputFile1>>tf[i];
        	inputFile2>>xi[i];
        	inputFile3>>vi[i];
        	inputFile4>>dt[i];
        	inputFile5>>tmax[i];



/* integration of ODE */
    while (ti <= tmax)
    {
    	tf[i] = ti[i] + dt[i];
    	euler2m(f1,f2,ti[i],xi[i],vi[i],tf[i],xf[i],vf[i]);
        cout<<"t="<<tf[i]<<"\t"<<"x="<<xf[i]<<"\t"<<"x'="<<vf[i]<<"\n";
        outputFile<<"t="<<tf[i]<<"\t"<<"x="<<xf[i]<<"\t"<<"x'="<<vf[i]<<"\n";
        ti[i] = tf[i];
        xi[i] = xf[i];
        vi[i] = vf[i];
    }
    }

    return 0;
}

/*
  Definition of the x'(t) = f1(t,x,x') = x' by the definition
*/
    double f1(double t, double x, double v)
{
    double d1x;
    d1x = v;
    return d1x;
}
/*
 *  Definition of the x"(t) = f2(t,x,x')
*/
    double f2(double t, double x, double v)
{
    double d2x;
    d2x = (t*t);
    return d2x;
}

//-----------------------------------------------------------------------

    double euler2m(double(*d1x)(double, double, double),
                   double(*d2x)(double, double, double),
                   double ti, double xi, double vi, double tf,
                   double& xf, double& vf)
    {
        xf= xi+ d1x(ti,xi,vi)*(tf-ti);
        vf= vi+ d2x(ti,xi,vi)*(tf-ti);
    /* correction */
        xf= xi+ (d1x(ti,xi,vi)+d1x(ti,xf,vf))*0.5*(tf-ti);
        vf= vi+ (d2x(ti,xi,vi)+d2x(ti,xf,vf))*0.5*(tf-ti);
       return 0.0;
    }
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