C++ Secant Method

Implementation of Secant Method written in C++.

IN
-3
-1
0.0000001
Out
X: -3 f(x): 2
X: -2 f(x): -1
X: -3 f(x): 2
X: -2.33333 f(x): -0.222222
X: -2.4 f(x): -0.04
X: -2.41463 f(x): 0.00118977
X: -2.41421 f(x): -6.00729e-06

// ? 2018 TheFlyingKeyboard and released under MIT License
// theflyingkeyboard.net

#include <iostream>
#include <math.h>

using namespace std;
static double function(double x);

int main() {
  double xn1; //x_(n - 1)
  double xn; //x_n
  double x;
  double precision;

  cout << "Enter beginning of interval: ";
  cin >> xn1;

  cout << "Enter end of interval: ";
  cin >> xn;

  cout << "Enter precision of method: ";
  cin >> precision;

  if (function(xn1) * function(xn) > 0.0f)
  {
    cout << "Function has same signs at ends of interval";
    return -1;
  }

  x = xn1;

  while (abs(function(x)) > precision) {
    cout << "X: " << x << " f(x): " << function(x) << endl;

    x = xn - ((function(xn) * (xn - xn1)) / (function(xn) - function(xn1)));
    xn1 = xn;
    xn = x;
  }

  int a;
  cin >> a; //Wait before exiting

  return 0;
}

static double function(double x) //x^2 + 2x -1
{
  return x * (x + 2) - 1;
}