问题三十七：C++怎么解一元四次方程？（2）——怎么解一元三次方程

37.2 怎么解一元三次方程？

用“盛金公式”求解：

----------------------------------------------main.cpp ------------------------------------------

main.cpp

float* roots_cubic_equation(float a, float b, float c, float d) {
    //the first element is the number of the real roots, and other elements are the real roots.
    //Shengjin's formula
    float *roots = new float[4];
    if (a == 0) {
        roots = roots_quadratic_equation(b, c, d);
    }
    else {
        float A = b*b - 3*a*c;
        float B = b*c - 9*a*d;
        float C = c*c - 3*b*d;
        float deita = B*B - 4*A*C;

        if ((A == B) && (A == 0)) {
            //the three roots are the same
            if (a != 0) {
                roots[1] = -b/(3*a);
            }
            else {
                if (b != 0) {