int gas=A0;
void setup() {

  pinMode(A0, INPUT);
  Serial.begin(9600);
  // put your setup code here, to run once:

}

void loop()
 {
  gas=analogRead(A0);
  int a=map(gas,0,1023,0,255);
  Serial.println(a);
  delay(1000);
  // put your main code here, to run repeatedly:

}