int sensorValue;
int num;


      void setup()
      {
          pinMode(2, OUTPUT);
          pinMode(3, OUTPUT);
          pinMode(4, OUTPUT);
          pinMode(5, OUTPUT);
          pinMode(6, OUTPUT);
          pinMode(7, OUTPUT);
          pinMode(8, OUTPUT);
          pinMode(9, OUTPUT);
          Serial.begin(9600);      // sets the serial port to 9600
       }


      void loop()
      {
        sensorValue = analogRead(0);       // read analog input pin 0
        
              if (sensorValue < 400)      // if there is little or no gas detected display blinking lights
              {
                
                  digitalWrite(2, LOW);
                  digitalWrite(3, LOW);
                  digitalWrite(4, LOW);
                  digitalWrite(6, LOW);
                  digitalWrite(7, LOW);
                  digitalWrite(8, LOW);
                  digitalWrite(9, LOW);
                
              digitalWrite(3, LOW);
              digitalWrite(8, HIGH);
              delay(500);
              digitalWrite(8, LOW);
              digitalWrite(6, HIGH);
              delay(500);
              digitalWrite(6, LOW);
              digitalWrite(3, HIGH);
              delay(500);
              }
              else
              {
                  if (sensorValue >= 900)               // the value of the gas measurement between 400 and 900 is displayed (this part refers to the cases below) 
                  {num = 9;}
                  else if (sensorValue >= 800)
                  {num = 8;}
                  else if (sensorValue >= 700)
                  {num = 7;}
                  else if (sensorValue >= 600)
                  {num = 6;}
                  else if (sensorValue >= 500)
                  {num = 5;}
                  else if (sensorValue >= 400)
                  {num = 4;} 
              }
              
              if (sensorValue > 700)                // if there is a lot of gas detected, the dot on the led display will blink
              {
              digitalWrite(5, HIGH);
              delay(100);
              digitalWrite(5, LOW);
              delay(100);
              }  
        
        
                  switch (num)
                  {
                  case 9:
                  digitalWrite(2, LOW);
                  digitalWrite(3, HIGH);
                  digitalWrite(4, HIGH);
                  digitalWrite(6, HIGH);
                  digitalWrite(7, HIGH);
                  digitalWrite(8, HIGH);
                  digitalWrite(9, HIGH);
                  break;
                  case 8:
                  digitalWrite(2, HIGH);
                  digitalWrite(3, HIGH);
                  digitalWrite(4, HIGH);
                  digitalWrite(6, HIGH);
                  digitalWrite(7, HIGH);
                  digitalWrite(8, HIGH);
                  digitalWrite(9, HIGH);
                  break;
                  case 7:
                  digitalWrite(2, LOW);
                  digitalWrite(3, LOW);
                  digitalWrite(4, HIGH);
                  digitalWrite(6, LOW);
                  digitalWrite(7, HIGH);
                  digitalWrite(8, HIGH);
                  digitalWrite(9, HIGH);
                  break;
                  case 6:
                  digitalWrite(2, HIGH);
                  digitalWrite(3, HIGH);
                  digitalWrite(4, HIGH);
                  digitalWrite(6, HIGH);
                  digitalWrite(7, HIGH);
                  digitalWrite(8, HIGH);
                  digitalWrite(9, LOW);
                  break;
                  case 5:
                  digitalWrite(2, LOW);
                  digitalWrite(3, HIGH);
                  digitalWrite(4, HIGH);
                  digitalWrite(6, HIGH);
                  digitalWrite(7, HIGH);
                  digitalWrite(8, HIGH);
                  digitalWrite(9, LOW);
                  break;
                  case 4:
                  digitalWrite(2, LOW);
                  digitalWrite(3, LOW);
                  digitalWrite(4, HIGH);
                  digitalWrite(6, HIGH);
                  digitalWrite(7, HIGH);
                  digitalWrite(8, LOW);
                  digitalWrite(9, HIGH);
                  break;
                  }
        
        
      }