int dirR = 12;
int speedR = 10;
int dirL = 13;
int speedL = 11;

void setup() 
{
  pinMode(dirR, OUTPUT);
  pinMode(speedR, OUTPUT);
  pinMode(dirL, OUTPUT);
  pinMode(speedL, OUTPUT);
}

void forward(int a, int b) //a=right motor, b=left motor
{
  digitalWrite(dirR, HIGH);
  analogWrite(speedR, a);
  digitalWrite(dirL, HIGH);
  analogWrite(speedL, b);
}

void backward(int a, int b) //a=right motor, b=left motor
{
  digitalWrite(dirR, LOW);
  analogWrite(speedR, a);
  digitalWrite(dirL, LOW);
  analogWrite(speedL, b);
}

void right(int a, int b) //a=right motor, b=left motor
{
  digitalWrite(dirR, LOW);
  analogWrite(speedR, a);
  digitalWrite(dirL, HIGH);
  analogWrite(speedL, b);
}

void left(int a, int b) //a=right motor, b=left motor
{
  digitalWrite(dirR, HIGH);
  analogWrite(speedR, a);
  digitalWrite(dirL, LOW);
  analogWrite(speedL, b);
}

void stop() 
{
  analogWrite(speedR, 0);
  analogWrite(speedL, 0);
}

void loop() 
{
  forward(100, 100); //forward
  delay(1000);
  stop();
  delay(1000);
  backward(100, 100); //backward
  delay(1000);
  stop();
  delay(1000);
}