Issue with secant root finding c++

I am trying to wirte a program for school that will use the secant root finding method. The equation is:

( v / b ) ^2sin(alpha)= kr * Ts^4 +Uc *Ts -q

and I have to find Ts.

Unfortunately the example i have been using as my base is not working for me :. The root it gives is -1.QNAN or something along those lines so i have a mistake in the secant method somewhere, I am a novice at C++ so i am having a lot of trouble fixing this. Any help will be appreciated, also if someone can tell me the codes to make it easier to post code, i would greatly appreciate it. Thanks here is my code so far:

#include <iostream>
#include <cmath>
#include <fstream>
#include <iomanip>

using namespace std;

void secant (double, double, double, double, double, double, double, double, double, double, double, int);

double fx(double, double, double, double, double, double, double);

const double tol=0.0001;    // Tolerance for convergence

const int max_iter=50;      // Maximum iterations allowed

int main ()
{
    double kr, uc, q, b, radians, Ts, x0, x1, root;
    int iteration; 
    const double PI = 4.0*atan(1.0);

    ifstream datain ("shuttle.txt");
    ofstream dataout ("results.txt");

    datain >> kr >> uc >> q >> b;

    int velocity = 16000;
    double angle =10;

    x0= 1000;
    x1 = 200;

    for (int velocity = 16000; velocity <= 17500; velocity += 500) {
        for (int angle = 10; angle <= 70; angle += 15) {
            radians= angle * PI/180  ;

            cout << velocity << endl;
            cout << radians << endl;
            cout << angle << endl;

           secant (angle, radians, velocity, kr, uc, q, b, Ts, x0, x1, root, iteration);    
        }
    }
    system("pause");

    return 0;
}

void secant(double angle, double radians, double velocity, double kr, double uc, double q, double b, double Ts, double x0, double x1, double root, int iteration) 
{
    double xnminus1, xnplus1, xn;
    iteration=0; 
    xnminus1=x0;
    xn=x1;

    do
    {
        ++iteration;
        xnplus1 = xn - fx(kr, uc, Ts, q, velocity, radians, xn)*(xn-xnminus1)/
                  (fx(kr, uc, Ts, q, velocity, radians,xn)-fx(kr, uc, Ts, q, velocity, radians,xnminus1));

        cout<<"x"<<iteration+1<<" = "<<xnplus1<<endl;

        xnminus1 = xn;

        xn=xnplus1;

    }  

    while ((fabs(fx(kr, uc, Ts, q, velocity, radians, xnplus1)) >= tol )&& (iteration < max_iter))
        ;    
    root=xnplus1;  

    cout<<"\nThe root is = "<<root<<endl;
    cout<<"The number of iterations was = "<<iteration<<endl;
    cout<<"The value of f(x) at the root = "<<fx(kr, uc, Ts, q, velocity, radians, root) <<endl<<endl;    
}

double fx(double kr, double uc, double Ts, double q, double velocity, double b, double radians)
{
    return kr * pow(Ts, 4.0) + uc * Ts - q - pow(velo开发者_开发问答city/b, 2.0) * sin(radians);
}

You use Ts without defining it. Funny that it is highlighted in blue... I think there is a senior SO user chuckling to himself somewhere...