light following car

int analogPin = 0;     // potentiometer wiper (middle terminal) connected to analog pin 3
                       // outside leads to ground and +5V
int raw = 0;           // variable to store the raw input value
int Vin = 5;           // variable to store the input voltage
float Vout = 0;        // variable to store the output voltage
float R1 = 10;         // variable to store the R1 value
float R2 = 0;          // variable to store the R2 value
float R3 = 0;          // variable to store the R3
float R4 = 0;          // variable to store the R4 value, change R2 to R3
float buffer = 0;      // buffer variable for calculation

void setup()
{
  Serial.begin(9600);             // Setup serial
  digitalWrite(13, HIGH);         // Indicates that the program has intialized
}

void loop()
{
  raw = analogRead(analogPin);    // Reads the Input PIN
  Vout = (5.0 / 1023.0) * raw;    // Calculates the Voltage on the Input PIN
  buffer = (Vin / Vout) - 1;
  R2 = R1 / buffer;
  delay(250);                     // time delay 1/4 second
  raw = analogRead(analogPin);    // Reads the Input PIN
  Vout = (5.0 / 1023.0) * raw;    // Calculates the Voltage on the Input PIN
  buffer = (Vin / Vout) - 1;
  R3 = R1 / buffer;
  R4 = (R3-R2);                   //R4 equals difference in R2 to R3
  if (R4 < 0)                     // switches output based on value on R4, if negative, else positive
{
  digitalWrite(11, LOW);
  digitalWrite(12, HIGH);
}
else
{
  digitalWrite(12,LOW);
  digitalWrite(11, HIGH);
}
  Serial.print("Voltage: ");      //
  Serial.println(Vout);           // Outputs the information
  Serial.print("R2: ");           //
  Serial.println(R2);             //
  Serial.print("R3: ");           //
  Serial.println(R3);             //
  Serial.print("R4: ");           //
  Serial.println(R4);             //
  delay(1000);
}
/*Credit to lxmyers for resistance input and buffer calculations
http://arduino.cc/forum/index.php/topic,21614.0.html*/