int laser=8;
int sensor=7;
int led=5;

void setup()
{
pinMode(laser,OUTPUT);
pinMode(led,OUTPUT);

pinMode(sensor,INPUT);

digitalWrite(laser,HIGH);
}

void loop()
{
int R=digitalRead(sensor);

if (R==LOW)
    digitalWrite(led,HIGH);
else
    digitalWrite(led,LOW);

delay(200);
}