#include<stdio.h>
#include<math.h>
void calroot(double a,double b,double c);
void main()
{
    double a,b,c;
    scanf("%f%f%f",&a,&b,&c);
    calroot(a,b,c);
}
void calroot(double a,double b,double c)
{
    double d,e,x1,x2;
    d=b*b-4*a*c;
    if (0==a)
       if (0==b)
          printf("方程无解\n");
       else
           printf("x1=x2=%f\n",-c/b);
    else if (0==d)
         printf("x1=x2=%f\n",-b/(2*a));
         else if (d>0)
             {
                 e=sqrt(d);
                 printf("x1=%f\n",(-b+e)/(2*a));
                 printf("x2=%f\n",(-b-e)/(2*a));
             }
             else
             printf("方程无实根");
             return 0;
}

错误的测试用例呢

你的变量e一个垃圾变量，不可能输出正确的答案的，属于语法错误，你可以对e变量初始化或者赋值

double 对应的是%lf float 才是%f