C语言：一元二次方程解的所有情况

从键盘任意输入a，b，c的值，编程计算并输出一元二次方程ax2+bx+c=0的根，当a=0时，输出“该方程不是一元二次方程”，当a≠0时，分b2−4ac>0、b2−4ac=0、b2−4ac<0三种情况计算并输出方程的根。
**输入格式要求："%f,%f,%f"  提示信息："Please enter the coefficients a,b,c:"
**输出格式要求："It is not a quadratic equation!\n"  "x1 = x2 = %.2f\n"  "x1 = %.2f, x2 = %.2f\n" 
"x1 = %.2f+%.2fi, "  "x2 = %.2f-%.2fi\n"
程序运行示例1如下：
Please enter the coefficients a,b,c:0,10,2
It is not a quadratic equation!
程序运行示例2如下：
Please enter the coefficients a,b,c:1,2,1
x1 = x2 = -1.00
程序运行示例3如下：
Please enter the coefficients a,b,c:2,3,2
x1 = -0.75+0.66i, x2 = -0.75-0.66i
变量定义为float类型，精度要求为1e-6，即
#define   EPS 1e-6

#include<stdio.h>
#include<math.h>
#define   EPS 1e-6
main() {
    float a, b, c, d, x1, x2, i;
    printf("Please enter the coefficients a,b,c:");
    scanf("%f,%f,%f", &a, &b, &c);
    d = b * b - 4 * a * c;
    if (fabs(a)<=0)
        printf("It is not a quadratic equation!\n");
    else 
    {
        if (d<0) 
        {
            x1 = -b / (2 * a);
            i = sqrt(-d) / (2 * a);
            printf("x1 = %.2f+%.2fi," , x1, i);
            printf("x2 = %.2f-%.2fi\n" , x1, i);
        } 
        else if (fabs(d) > EPS) 
        {
            x1 = (-b + sqrt(d)) / (2 * a);
            x2 = (-b - sqrt(d)) / (2 * a);
            printf("x1 = %.2f, x2 = %.2f\n", x1, x2);
        } 
        else if (fabs(d)<=EPS)
            printf("x1 = x2 = %.2f\n", -b / (2 * a));
    }

}