Object Avoiding Bot

1byte la=2,lb=3,ra=5,rb=4,trig=6,echo=7,ls=8,rs=9;
2float duration=1,distance;
3float  d;
4void setup() {
5  pinMode(la,OUTPUT);
6  pinMode(lb,OUTPUT);
7  pinMode(ra,OUTPUT);
8  pinMode(rb,OUTPUT);
9  pinMode(trig,OUTPUT);
10  pinMode(echo,INPUT);
11  pinMode(ls,INPUT);
12  pinMode(rs,INPUT);
13  Serial.begin(9600);
14}
15float dis(){
16 digitalWrite(trig,LOW);
17  delayMicroseconds(2);
18 digitalWrite(trig,HIGH);
19 delayMicroseconds(10); 
20  digitalWrite(trig,LOW);
21 duration=pulseIn(echo,HIGH);
22 distance=duration*(0.034/2);
23  Serial.print("distance =");
24 Serial.println(distance);
25 return distance;
26  delay(1000);
27}
28void drive(){
29  digitalWrite(ra,1);
30  digitalWrite(la,1);
31  digitalWrite(lb,0);
32  digitalWrite(rb,0);
33}
34void stoper(){
35  digitalWrite(ra,0);
36  digitalWrite(la,0);
37  digitalWrite(lb,0);
38  digitalWrite(rb,0);
39}
40void  reverse(){
41  digitalWrite(ra,0);
42  digitalWrite(la,0);
43  digitalWrite(lb,1);
44  digitalWrite(rb,1);
45}
46void right(){
47  digitalWrite(ra,0);
48  digitalWrite(la,1);
49  digitalWrite(lb,0);
50  digitalWrite(rb,1);
51}
52void left(){
53  digitalWrite(ra,1);
54  digitalWrite(la,0);
55  digitalWrite(lb,1);
56  digitalWrite(rb,0);
57}
58void  loop() {
59 d=dis();
60 drive();
61 if(d<=15)
62 {
63  if(digitalRead(ls)==1  && digitalRead(rs)==0)
64  {
65    stoper();
66    delay(1000);
67    reverse();
68    delay(1000);
69    right();
70    delay(500);
71    stoper();
72  }
73  else
74  if(digitalRead(rs)==1 && digitalRead(ls)==0)
75  {
76    stoper();
77    delay(1000);
78    reverse();
79    delay(1000);
80    left();
81    delay(500);
82    stoper();
83  }
84  else
85  {
86    stoper();
87    delay(1000);
88    reverse();
89    delay(1000);
90    right();
91    delay(2000);
92  }
93 }
94 else
95 if(digitalRead(ls)==1  || digitalRead(rs) ==1)
96 {
97  if(digitalRead(ls)==1)
98  {
99    stoper();
100    delay(1000);
101    reverse();
102    delay(1000);
103    right();
104    delay(500);
105  }
106  else
107  {
108    stoper();
109    delay(1000);
110    reverse();
111    delay(1000);
112    left();
113    delay(500);
114  }
115 }
116}
117