C++ using E in a mathematical equation

Question

I'm trying to solve aX² + bX + c = 0 but I can't seem to make it work with using the math header (which I'm not supposed to use).

printf("%E",(-b+(b*b-4*a*c)E0.5)/2a);

Answer 1

Use std::sqrt from header <cmath>. Also, you must write (2 * a), not 2a.

Another thing: don't use the textbook formula for solving quadratic equations. Use the method described there.

If you can't use the math header, then you have to implement the square root eg. as described there:

double my_abs(double x)
{
    return x > 0 ? x : -x;
}

double my_sqrt(double x)
{
    static const double eps = 1e-12;
    double u = x, uold;

    do { uold = u; u = (u * u + x) / (2 * u); }
    while (my_abs(u - uold) < eps * x);

    return u;
}