void solv_quadr_equa (float a,float b,float c)
{
    if(a==0)
        if(b==0)
            printf("no answer due to input error\n");
        else
            printf("the single root is %f\n",-c/b);
    else
    {double disc,twoa,term1,term2;
    disc=b*b-4*a*c;
    twoa=2*a;
    term1=-b/twoa;
    term2=sqrt (fabs (disc)/twoa;
    if(disc<0.0)
        printf("complex root:\n real part=%f,imag part=%f\n",term1,term2);
    else
        printf("real root:\n root1=%f,root2=%f\n",term1+term2,term1-term2);
        
        }

不明白你什么意思！

term2=sqrt (fabs (disc)/twoa   少了个括号。
这个就是个解二次方程的函数，随便来个主函数就可以了