一元二次方程式

[Muscovy (Muscovy)]

        作業雖然寫過了, 反正考試也還是要會...

        底下是一種大程式常用的基本結構.
        初學的人極有可能會看不下去...
        可是真正程式寫大了很容易就長這副德性.

        看不下去的, 看 main() 裡頭的 switch-case 就好.

# include <stdio.h>
# include <stdlib.h>
# include <math.h>

# define EQT_X_MANY     1
# define EQT_X_NONE     2
# define EQT_X_LINEAR   3
# define EQT_X_QUADRIC  4
# define EQT_X_COMPLEX  5
# define EPSILON        1.0E-6

# define fiszero(x)     (fcmp(x, 0.0) == 0)

int getceff(double [3]);
int solve_linear(double t[2], double *x);
int solve_quadric(double t[3], double *x1, double *x2);
int fcmp(double, double);

int main()
{
    double      t[3], x1, x2;
    int         type;

        getceff(t);

        type = !fiszero(*t)
                ? solve_quadric(t, &x1, &x2) : solve_linear(t + 1, &x1);

        switch (type)   {
        case EQT_X_MANY:
                puts("X has many solutions.");
         break;
        case EQT_X_NONE:
                puts("X has no solution.");
         break;
        case EQT_X_LINEAR:
                printf("Linear: X = %.4f.\n", x1);
         break;
        case EQT_X_QUADRIC:
                printf("Quadric: X = %.4f, %.4f.\n", x1, x2);
         break;
        case EQT_X_COMPLEX:
                printf("Quadric/Complex: "
                        "X = %.4f + %.4fi, %.4f - %.4fi.\n",
                        x1, x2, x1, x2
                );
         break;
        default:
                puts("ERROR: Equation type unknown!");
        }

    return 0;
}

int fcmp(double x, double y)
{
    double      diff;

        diff = x && y ? (x - y) / fabs(x) : x + y;

    return (diff > EPSILON) - (diff < -EPSILON);
}

int solve_linear(double t[2], double *x)
{
    return fiszero(*t) ? (fiszero(t[1]) ? EQT_X_MANY : EQT_X_NONE) :
                (*x = -t[1] / t[0], EQT_X_LINEAR);
}

int solve_quadric(double t[3], double *x1, double *x2)
{
    double      a = t[0], b = t[1], c = t[2];
    double      f, g;

        f = b * b - 4 * a * c, g = sqrt(fabs(f)) / (2 * a);
        b /= -2 * a;

        *x1 = b - (fcmp(f, 0) >= 0 ? g : 0);
        *x2 = g + (fcmp(f, 0) >= 0 ? b : 0);

    return f >= 0 ? EQT_X_QUADRIC : EQT_X_COMPLEX;
}

int getceff(double t[3])
{
        printf("Solving ax^2 + bx + c = 0.\n"
                "Input (a, b, c) as type double, "
                "separated by while spaces.\n"
        );

        if (scanf("%lf%lf%lf", t, t + 1, t + 2) < 3)    {
                puts("Invalid arguments. Exiting...");
                exit(1);
        }

        printf("Equation: %.4fx^2 + %.4fx + %.4f = 0.\n\n",
                t[0], t[1], t[2]);

    return 0;
}


--

  新詩練習：新鮮。踩破初春裡的狗大便；不經意的滄桑，滿溢著嫩黃的喜悅。

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