void setup(){
  kwadratischevgl();
}
void loop() {
}
void kwadratischevgl(){
  Serial.begin(9600);
  int a;
  int b;
  int c;
  int D;
  Serial.println("Voer waarden in van a, b, c van de kwadratische vergelijking (aX^2 + bX + c):");
  while (Serial.available() == 0){}
  a = Serial.parseInt();
  Serial.print(a);
  Serial.print("x^2 + ");
  ClearBuffer();
  while (Serial.available() == 0){}
  b = Serial.parseInt();
  Serial.print(b);
  Serial.print("x + ");
  ClearBuffer();
  while (Serial.available() == 0){}
  c = Serial.parseInt();
  Serial.println(c);
  ClearBuffer();
  D = pow(b, 2) -4*(a*c);
  switch (D) {
    case 0: 
      Serial.print(-b/(2*a));
      break;
    case 1 ... 1000:
      Serial.print("x1 = ");
      Serial.println((-b-sqrt(D))/(2*a));
      Serial.print("x2 = ");
      Serial.println((-b+sqrt(D))/(2*a));
      break;
    case -1000 ... -1:
      Serial.print("x1 = ");
      Serial.print(-b/(2*a));
      Serial.print(" + i");
      Serial.println(sqrt(D)/(2*a));
      Serial.print("x2 = ");
      Serial.print(-b/(2*a));
      Serial.print(" - i");
      Serial.print(sqrt(D)/(2*a));

  }

}

void ClearBuffer(){
  while(Serial.available()){
    Serial.read();
  }
}