Arduino robot follow the object

1#include <AFMotor.h>   
2
3AF_DCMotor MotorL(4);  // motor for drive  Left on M4
4AF_DCMotor MotorR(3);  // motor for drive Right on M3
5
6//ultrasonic  setup:
7 const int trigPin = A4; // trig pin connected to Arduino's pin A4
8  const int echoPin = A5; // echo pin connected to Arduino's pin A5
9
10// defines  variables
11long duration;
12int distanceCm=0;
13
14int distanceKeep = 8;
15
16void  setup() {
17  Serial.begin(115200);      // set up Serial library at 115200 bps
18  Serial.println("robot Follow Object Mod");
19  pinMode(trigPin, OUTPUT);  //  Sets the trigPin as an Output
20  pinMode(echoPin, INPUT);   // Sets the echoPin  as an Input
21
22  // Set the speed to start, from 0 (off) to 255 (max speed)
23  // sometimes the motors don't have the same speed, so use these values tomake  your robot move straight
24  MotorL.setSpeed(125);
25  MotorR.setSpeed(125);
26  // turn off motor
27  MotorL.run(RELEASE);
28  MotorR.run(RELEASE);
29}
30
31//  main program loop
32void loop() {
33 distanceCm=getDistance(); //variable to store  the distance measured by the sensor
34   
35 Serial.println(distanceCm); //print  the distance that was measured
36
37  //if the distance is less than 5cm, robot  will go backward for 1 second, and turn right for 1 second
38  if(distanceCm <  distanceKeep && distanceCm >= 5){
39    MotorL.run(BACKWARD);
40    MotorR.run(BACKWARD);
41  } 
42  if(distanceCm > (distanceKeep+3) && distanceCm < (distanceKeep+20)){
43    MotorL.run(FORWARD);
44    MotorR.run(FORWARD);
45  } 
46  if(distanceCm  > (distanceKeep+20)){
47    MotorL.run(FORWARD); 
48    MotorR.run(BACKWARD);
49  }
50  if(distanceCm >= distanceKeep && distanceCm <= (distanceKeep+3)){
51    MotorL.run(RELEASE);
52    MotorR.run(RELEASE);
53  }
54}
55
56
57
58//RETURNS THE DISTANCE MEASURED  BY THE HC-SR04 DISTANCE SENSOR
59int getDistance() {
60  int echoTime;                   //variable  to store the time it takes for a ping to bounce off an object
61  int calcualtedDistance;         //variable to store the distance calculated from the echo time
62  
63  //send out an ultrasonic pulse that's 10ms long
64  digitalWrite(trigPin, HIGH);
65  delayMicroseconds(10); 
66  digitalWrite(trigPin, LOW);
67
68  echoTime = pulseIn(echoPin,  HIGH);      //use the pulsein command to see how long it takes for the
69                                          //pulse  to bounce back to the sensor
70
71  calcualtedDistance = echoTime / 58.26;  //calculate  the distance of the object that reflected the pulse (half the bounce time multiplied  by the speed of sound)
72  return calcualtedDistance;              //send back  the distance that was calculated
73}
74