L293D CODE

// Use this code to test your motor with the Arduino board:

// if you need PWM, just use the PWM outputs on the Arduino
// and instead of digitalWrite, you should use the analogWrite command

// --------------------------------------------------------------------------- Motors
int motor_left[] = {3,8};
int motor_right[] = {12, 7};

// --------------------------------------------------------------------------- Setup
void setup() {
Serial.begin(9600);

// Setup motors
int i;
for(i = 0; i < 2; i++){
pinMode(motor_left[i], OUTPUT);
pinMode(motor_right[i], OUTPUT);
}

}

// --------------------------------------------------------------------------- Loop
void loop() {

drive_forward();
delay(1000);
motor_stop();
Serial.println("1");

drive_backward();
delay(1000);
motor_stop();
Serial.println("2");

turn_left();
delay(1000);
motor_stop();
Serial.println("3");

turn_right();
delay(1000);
motor_stop();
Serial.println("4");

motor_stop();
delay(1000);
motor_stop();
Serial.println("5");
}

// --------------------------------------------------------------------------- Drive

void motor_stop(){
digitalWrite(motor_left[0], LOW);
digitalWrite(motor_left[1], LOW);

digitalWrite(motor_right[0], LOW);
digitalWrite(motor_right[1], LOW);
delay(25);
}

void drive_forward(){
digitalWrite(motor_left[0], HIGH);
digitalWrite(motor_left[1], LOW);

digitalWrite(motor_right[0], HIGH);
digitalWrite(motor_right[1], LOW);
}

void drive_backward(){
digitalWrite(motor_left[0], LOW);
digitalWrite(motor_left[1], HIGH);

digitalWrite(motor_right[0], LOW);
digitalWrite(motor_right[1], HIGH);
}

void turn_left(){
digitalWrite(motor_left[0], LOW);
digitalWrite(motor_left[1], HIGH);

digitalWrite(motor_right[0], HIGH);
digitalWrite(motor_right[1], LOW);
}

void turn_right(){
digitalWrite(motor_left[0], HIGH);
digitalWrite(motor_left[1], LOW);

digitalWrite(motor_right[0], LOW);
digitalWrite(motor_right[1], HIGH);
}


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IRRELEVANT 

Beside this code u can also take help



// Use this code to test your motor with the Arduino board:

// if you need PWM, just use the PWM outputs on the Arduino
// and instead of digitalWrite, you should use the analogWrite command

// --------------------------------------------------------------------------- Motors
int motor_left[] = {2, 3};
int motor_right[] = {7, 8};

// --------------------------------------------------------------------------- Setup
void setup() {
Serial.begin(9600);

// Setup motors
int i;
for(i = 0; i < 2; i++){
pinMode(motor_left[i], OUTPUT);
pinMode(motor_right[i], OUTPUT);
}

}

// --------------------------------------------------------------------------- Loop
void loop() { 

drive_forward();
delay(1000);
motor_stop();
Serial.println("1");

drive_backward();
delay(1000);
motor_stop();
Serial.println("2");

turn_left();
delay(1000);
motor_stop();
Serial.println("3");

turn_right();
delay(1000);
motor_stop();
Serial.println("4"); 

motor_stop();
delay(1000);
motor_stop();
Serial.println("5");
}

// --------------------------------------------------------------------------- Drive

void motor_stop(){
digitalWrite(motor_left[0], LOW); 
digitalWrite(motor_left[1], LOW); 

digitalWrite(motor_right[0], LOW); 
digitalWrite(motor_right[1], LOW);
delay(25);
}

void drive_forward(){
digitalWrite(motor_left[0], HIGH); 
digitalWrite(motor_left[1], LOW); 

digitalWrite(motor_right[0], HIGH); 
digitalWrite(motor_right[1], LOW); 
}

void drive_backward(){
digitalWrite(motor_left[0], LOW); 
digitalWrite(motor_left[1], HIGH); 

digitalWrite(motor_right[0], LOW); 
digitalWrite(motor_right[1], HIGH); 
}

void turn_left(){
digitalWrite(motor_left[0], LOW); 
digitalWrite(motor_left[1], HIGH); 

digitalWrite(motor_right[0], HIGH); 
digitalWrite(motor_right[1], LOW);
}

void turn_right(){
digitalWrite(motor_left[0], HIGH); 
digitalWrite(motor_left[1], LOW); 

digitalWrite(motor_right[0], LOW); 
digitalWrite(motor_right[1], HIGH); 
}

For IR sensor

int analogPin = 3;     // Infrared Sensor (Right lead) connected to analog pin 3
                                    // outside leads to ground and +5V
int val = 0;                  // variable to store the value read

void setup()
{
  Serial.begin(9600);          //  setup serial
}

void loop()
{
  val = analogRead(analogPin);    // read the input pin
  Serial.println(val);                           // debug value
}

Program for Forward motion when Infra Red Sensor Value is smaller than 100

// This is the basic code which runs a loop that makes the Robot go straight forward when the Infrared value is below 100.

int analogPin = 3;     // Infrared Sensor (Right lead) connected to analog pin 3
                                     // Infrared Sensor(middle Lead) connected to +5V
                                     // Infrared Sensor(Left Lead) connected to ground
                             
int val = 0;           // variable to store the value read


int LeftMotorForward = 10; // Pin 10 has Left Motor connected on Arduino boards.
int LeftMotorReverse = 9; // Pin 9 has Left Motor connected on Arduino boards.

int RightMotorForward = 12; // Pin 12 has Right Motor connected on Arduino boards.
int RightMotorReverse = 13; // Pin 13 has Right Motor connected on Arduino boards.

//------------------------------------------------------------------------------------------------

void setup()
{
  pinMode(LeftMotorForward, OUTPUT);  // initialize the  pin as an output.
  pinMode(RightMotorForward, OUTPUT);  // initialize the  pin as an output.
  pinMode(LeftMotorReverse, OUTPUT);  // initialize the  pin as an output.
  pinMode(RightMotorReverse, OUTPUT);  // initialize the  pin as an output.

   Serial.begin(9600);          //  setup serial
}

// The following Loop is to make the Robot go staright when the Infrared value is below 100

void loop()

{
   val = analogRead(analogPin);    // read the input pin
  Serial.println(val);             // debug value

  if (val <100)

// If the read value is < 100 then run the code below which will turn  both Left and Right Motor on making the Robot go straight.

  {
   digitalWrite(RightMotorForward, HIGH);   // turn the Right Motor ON
   digitalWrite(LeftMotorForward, HIGH);   // turn the Left Motor ON
   delay(10000);               // wait for  10 seconds

   digitalWrite(RightMotorForward,LOW);   // turn the Right Motor OFF
   digitalWrite(LeftMotorForward, LOW);   // turn the Left Motor OFF
   delay(10000);               // wait for  10 seconds
  }

}

program when Infrared Red sensor Value is smaller than 100

When IR Value is Less than 100 then the Motors are turned on and the Robot drives forward for 10 seconds.