Error Compiling tof Board

Heres the whole thing Bob, I appreciate your help.

//First attempt at making a 4 zone auto watering system
//potPins values are just for setup purposes, must be calibrated once placed in soil
//potPins are to adjust the high and low moisture ranges for each zone
//must be used with Arduino Mega

const int zone1 = A0;
const int zone2 = A1;
const int zone3 = A2;
const int zone4 = A3;

const int potLow = A4;
const int potHigh = A5;

const int valve1 = 2;
const int valve2 = 3;
const int valve3 = 4;
const int valve4 = 5; 


void setup()
  {
   pinMode(valve1,OUTPUT);
   pinMode(valve2,OUTPUT);
   pinMode(valve3,OUTPUT);
   pinMode(valve4,OUTPUT);
  }

void loop()
  {
    if(analogRead(zone1) <= potLow){           //read the value from the soil moisture sensor
      digitalWrite(valve1,HIGH);}              //open the valve
      if(analogRead(zone1) >= potHigh){        //when value from soil moisture sensor reaches the upper limit
        digitalWrite(valve1,LOW);              //close the valve
      }
    }