#include<stdio.h>
#include<math.h>
void main()
{
    float a,b,c,x1,x2,disc;
    printf("please input a,b,c:");
    scanf("%d%d%d",&a,&b,&c);
    if(fabs(a)<1e-6)  //我把这个红色的1e-6唤作为“0”，为什么运行的结果就变了？
        printf("The equation is not a quadratic\n");
    else
    {
        disc=b*b-4*a*c;
        if(disc<0)
            printf("The equation has not real root\n");
        else
            if(fabs(disc)<0)
                printf("The equation has two equal roots:%8.4f\n",-b/(2*a));
            else
            {x1=(-b+sqrt(disc))/(2*a);
             x2=(-b-sqrt(disc))/(2*a);
             printf("The equation has distinct real roots:%8.4f,%8.4f\n",x1,x2);
            }
    }
}