/* p2_2.c */
#include <stdio.h>
#include <math.h>

int ratkaise_2_asteen_yhtalo(double *x1, double *x2,
  double a, double b, double c)
{
  double D,SD;
  *x1 = *x2 = 0;
  if ( a==0 ) {                       /*       bx + c = 0 */
    if ( b==0 ) {                     /*            c = 0 */
      if ( c==0 ) {                   /*            0 = 0 */
        return 0;                     /* id. tosi         */
      }                 /* c==0 */
      else {            /* c!=0 */    /*       0 != c = 0 */
        return 1;                     /* Aina ep„t.       */
      }                 /* c!=0 */
    }                   /* b==0 */
    else {              /* b!=0 */    /*       bx + c = 0 */
      *x1 = *x2 = -c/b;
      return 0;
    }                   /* b!=0 */
  }                     /* a==0 */
  else {                /* a!=0 */    /* axx + bx + c = 0 */
    D = b*b - 4*a*c;
    if ( D>=0 ) {                     /* Reaaliset juuret */
      SD  = sqrt(D);
      *x1 = (-b-SD)/(2*a);
      *x2 = (-b+SD)/(2*a);
      return 0;
    }                   /* D>=0 */
    else {                            /* Imag. juuret     */
      return 1;
    }                   /* D<0  */
  }                     /* a!=0 */
}

double P2(double x, double a, double b, double c)
{
  return (a*x*x + b*x + c);
}

int main(void)
{
  double a,b,c,x1,x2;
  do {
    printf("Anna 2. asteen yht„l”n a b c >");
    scanf("%lf %lf %lf",&a,&b,&c);
    if ( ratkaise_2_asteen_yhtalo(&x1,&x2,a,b,c) ) {
      printf("Yht„l”ll„ ei ole reaalisia juuria!\n");
    }
    else {
      printf("1. ratkaisu on %lf.  "
             "Arvoksi tulee t„ll”in %lf.\n",x1,P2(x1,a,b,c));
      printf("2. ratkaisu on %lf.  "
             "Arvoksi tulee t„ll”in %lf.\n",x2,P2(x2,a,b,c));
    }
  } while (a>0);
  return 0;
}

&&