Sewage treatment plant

#define SensorPin A2            //pH meter Analog output to Arduino Analog Input 0
#define Offset 15.76      //deviation compensate
#define LED 13
#define samplingInterval 20
#define printInterval 800
#define ArrayLenth  40    //times of collection
#define uart  Serial
int pHArray[ArrayLenth];   //Store the average value of the sensor feedback
int pHArrayIndex = 0;
void setup(void)
{
  pinMode(LED, OUTPUT);
  uart.begin(9600);
  uart.println("pH meter experiment!");    //Test the uart monitor
}
void loop(void)
{
  static unsigned long samplingTime = millis();
  static unsigned long printTime = millis();
  static float pHValue, voltage;
  if (millis() - samplingTime > samplingInterval)
  {
    pHArray[pHArrayIndex++] = analogRead(SensorPin);
    if (pHArrayIndex == ArrayLenth)pHArrayIndex = 0;
    voltage = avergearray(pHArray, ArrayLenth) * 5.0 / 1024;
    pHValue = -5.882 * voltage + Offset;
    samplingTime = millis();
  }
  if (millis() - printTime > printInterval)  //Every 800 milliseconds, print a numerical, convert the state of the LED indicator
  {
    uart.print("Voltage:");
    uart.print(voltage, 2);
    uart.print("    pH value: ");
    uart.println(pHValue, 2);
    digitalWrite(LED, digitalRead(LED) ^ 1);
    printTime = millis();
  }
}
double avergearray(int* arr, int number) {
  int i;
  int max, min;
  double avg;
  long amount = 0;
  if (number <= 0) {
    uart.println("Error number for the array to avraging!/n");
    return 0;
  }
  if (number < 5) { //less than 5, calculated directly statistics
    for (i = 0; i < number; i++) {
      amount += arr[i];
    }
    avg = amount / number;
    return avg;
  } else {
    if (arr[0] < arr[1]) {
      min = arr[0]; max = arr[1];
    }
    else {
      min = arr[1]; max = arr[0];
    }
    for (i = 2; i < number; i++) {
      if (arr[i] < min) {
        amount += min;      //arr<min
        min = arr[i];
      } else {
        if (arr[i] > max) {
          amount += max;  //arr>max
          max = arr[i];
        } else {
          amount += arr[i]; //min<=arr<=max
        }
      }//if
    }//for
    avg = (double)amount / (number - 2);
  }//if
  return avg;
}

#include <SoftwareSerial.h>

SoftwareSerial mySerial(10, 11); // RX, TX

char w;

void setup() {
  Serial.begin(9600);
  mySerial.begin(9600);
  delay(1000); //wait to start the device properly
}

void loop() {
  if (mySerial.available()) {
    w = mySerial.read();
    Serial.println(w);  //PC
    delay(10);
    //commands with Serial.println(); show on pc serial monitor
  }

  if (Serial.available()) {
    w = Serial.read();
    mySerial.println(w); //Phone
    delay(10);
    //commands with mySerial.println(); show on the device app
  }

//shown on pc
Serial.println("This is a test run");
Serial.println("Congratulations! Device Connected!");
Serial.println();

//shown on device app
mySerial.println("This is a test run");
mySerial.println("Congratulations! Device Connected!");
mySerial.println();

delay(2000);
}