程序代码：

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main()
{
    float a,b,c,d,d2,d3,d4,result1,result2;
    printf("Please input three float numbers:");
    scanf("%f %f %f",&a,&b,&c);
    d=b*b-4*a*c;
    if(a==0)
    {
        printf("The equation is not quadratic.");
    }
    else
    {
        if(d>0)
        {
            d2=sqrt(d);
            result1=(-b+d2)/(2*a);
            result2=(-b-d2)/(2*a);
            printf("The equation has two distinct real roots:%.4f and %.4f",result1,result2);
        }
        else if(d<0)
        {
            d3=sqrt(-d);
            d4=(-b)/(2*a);
            printf("The equation has two complex roots:%.4f+%.4fi and %.4f-%.4fi",d4,d3,d4,d3);
        }
        else
        {
            d2=sqrt(d);
            result1=(-b+d2)/(2*a);
            printf("The equation has two equal roots:%.4f",result1);
        }
    }
    systems("pause");
    return 0;
}