程序代码：

/*一个解一元二次方程输入a,b,c求x1和x2!!!!*/

# include <stdio.h>

# include <math.h>

int main(void)

{   double a, b, c, x1, x2, derta;

    printf ("请输入二次方程的系数a,b,c用回车键隔开\n");

    scanf ("%lf%lf%lf",&a,&b,&c);

    derta = b*b - 4*a*c;

    if (derta >= 0)

    {  x1 = (-b + sqrt(derta)) / 2*a;

       x2 = (-b + sqrt(derta)) / 2*a;

       printf ("x1的值是：%lf\n",x1);

       printf ("x2的值是：%lf\n",x2);

    }

    else 

        printf ("次方程无解！！！\n");

     return 0;

}