题解 | #计算一元二次方程#

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

int main() {

    double a = 0;//初始化
    double b = 0;
    double c = 0;
    while (scanf("%lf %lf %lf", &a, &b, &c) != EOF) //多组输入
    {
        double w = b * b - 4 * a * c; //判别式公式
        double p1 = (-b+0) - sqrt(w);//+0防止精度误差
        double p2 = (-b+0) + sqrt(w);
        double xa = p1 / (2 * a);//x1
        double xb = p2 / (2 * a);//x2

        if (a == 0)//a=0
        {
            printf("Not quadratic equation\n");
        } 
        else if (a != 0)
        {
            if (w == 0.0)
            {
                if (a > 0)//p1精度出现误差
                {
                    printf("x1=x2=%.2lf\n", xa);         
                }
                if (a < 0)//xa,xb精度出现误差
                {
                    printf("x1=x2=%.2lf\n", (-b)/(2*a));         
                }
            }
            if (w > 0.0)
            {
                printf("x1=%.2f;x2=%.2f\n", xa, xb);         
            }
            if (w < 0.0)
            {
                float actual = -b / (2 * a);
                float virtual = sqrt(-w) / (2 * a);
                printf("x1=%.2f-%.2fi;x2=%.2f+%.2fi\n", actual, virtual, actual, virtual);
            }
        }
    }    

    return 0;
}