First, we declare our sensor and servo. Then, we initialize our setup() function.

#include <Servo.h>      
                            
Servo servo;                                     
#define Svo_Pin   9 
#define GP2Y0A21  A0 
 
void setup() {   
  servo.attach(Svo_Pin);                        
  Serial.begin(9600);   
} 

In the loop() function, we move our servo from degree 0 to 180. On each degree change, we read a distance value from the sensor. Then, we calculate the distance by calling the get_gp2d12() function, defined in this sketch. Lastly, we print the resulting measurement to the serial port.

void loop() { 
  for (int i=0;i<180;i++)           
  { 
    servo.write(i); 
    uint16_t value = analogRead(GP2Y0A21); 
    uint16_t range = get_gp2d12(value);     
    Serial.print("Distance. Value: "); 
    Serial.print(value);   
    Serial.print(". Range: "); 
    Serial.print(range);   
    Serial.println(" mm"); 
 
    delay(200); 
  } 
  delay(2000); 
} 

To calculate a distance, we can refer to the datasheet. We'll implement the get_gp2d12() function to obtain a distance value:

uint16_t get_gp2d12 (uint16_t value) { 
  if (value < 10) value = 10; 
  return ((67870.0 / (value - 3.0)) - 40.0); 
}