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

using namespace std;

class cubic
{
public:
    double a,b,c,d;
    double A, B, C, Y1, Y2, T, theta;
    double delta,root1;
    typedef struct xushu
    {
        double shibu;
        double xubu;
    }xushu;
    xushu root2, root3;

    void rooting()
    {
        cout << "Please input coefficients a, b, c and d respectively to calculate roots." << endl;
        cout << "The coefficient a is: ";
        cin >> a;
        cout << "The coefficient b is: ";
        cin >> b;
        cout << "The coefficient c is: ";
        cin >> c;
        cout << "The coefficient d is: ";
        cin >> d;
        A = pow(b,2)-3*a*c;
        B = b*c-9*a*d;
        C = pow(c,2)-3*b*d;
        delta = pow(B,2)-4*A*C;
        if (A==B&&A==0&&B==0)
        {
            root1 = -b/(3*a);
            root2.shibu = -c/b;
            root3.shibu = -3*d/c;
        }
        else if (delta > 0)
        {
            Y1 = A*b+3*a*(-B+pow((pow(B,2)-4*A*C),(1.0/2)))/2;
            Y2 = A*b+3*a*(-B-pow((pow(B,2)-4*A*C),(1.0/2)))/2;
            root1 = (-b-pow(Y1,(1.0/3))-pow(Y2,(1.0/3)))/(3*a);
            root2.shibu = (-2*b+pow(Y1,(1.0/3))+pow(Y2,(1.0/3)))/(6*a);
            root2.xubu = (pow(3,(1.0/2))*(pow(Y1,(1.0/3))-pow(Y2,(1.0/3))))/(6*a);
            root3.shibu = (-2*b+pow(Y1,(1.0/3))-pow(Y2,(1.0/3)))/(6*a);
            root3.xubu = (-pow(3,(1.0/2))*(pow(Y1,(1.0/3))-pow(Y2,(1.0/3))))/(6*a);
            cout << root1 << root2.shibu << root2.xubu << root3.shibu << root3.xubu << endl;
        }
        else if (delta == 0 && A != 0)
        {
            root1 = -b/a+(B/A);
            root2.shibu = root3.shibu = -(B/A)/2;
            cout << root1 << root2.shibu << root3.shibu << endl;
        }
        else if (delta < 0 && A>0 && T>-1 && T<1)
        {
            T=(2*A*b-3*a*B)/(pow(2*A,(3/2)));
            theta = acos(T);
            root1 = (-b-pow(2*A,(1.0/2))*cos(theta/3))/(3*a);
            root2.shibu = (-b+pow(A,(1.0/2))*(cos(theta/3))+(pow(3,(1.0/2)*sin(theta/3))))/(3*a);
            root3.shibu = (-b+pow(A,(1.0/2))*(cos(theta/3))-(pow(3,(1.0/2)*sin(theta/3))))/(3*a);
            cout << root1 << root2.shibu << root3.shibu << endl;
        }
    }
}calCubic;

[ 本帖最后由 spikespiegel 于 2010-11-17 17:05 编辑 ]

能说明是啥问题吗？

编译出来后输入4个系数 然后结果显示的一律是-1.#IND 不过好像能判断根的数量