Unlock your door with a knock

// Basically the code hear and save the knock and compare it to any other knock to open the door

#include <OneSheeld.h>
int pin1 = 9;
int pin2 = 10;
int pin3 = 11;
int pin4 = 12;
int led4 = 13;
int counter = 0;
int sec = 0;
int hear[20] = {};
int saved[20] = {};
int flagc = 0;
int flags = 0;
int flagf = 0;
int i = 0;
int ii = 0;

void setup()
{
  OneSheeld.begin();
  pinMode(pin1,OUTPUT);
  pinMode(pin2,OUTPUT);
  pinMode(pin3,OUTPUT);
  pinMode(pin4,OUTPUT);
  pinMode(led4,OUTPUT);
}
void loop()
{
  if (Keypad.isRowPressed(0) && Keypad.isColumnPressed(3))
  {
    set();
  } 
  else if (Keypad.isRowPressed(1) && Keypad.isColumnPressed(3))
  {
    record();
  }
  else if (Keypad.isRowPressed(2) && Keypad.isColumnPressed(3))
  {
    check();
  }
  else {
    flagf = 0;
    digitalWrite(pin1,LOW);
    digitalWrite(pin2,LOW);
    digitalWrite(pin3,LOW);
    digitalWrite(pin4,LOW);
    digitalWrite(led4,LOW);
  }  
}

void clc ()
{
  counter = 0;
  for (int i=0; i<=20;i++)
  {
    hear[i] = 0;
    saved[i] = 0;
  }
  i = 0;
  ii = 0;
  digitalWrite(led4,LOW); 
}

void set()
{
  if (flagf == 0)
  {
  clc();
  }
  if(Mic.getValue() > 80 && flags == 0)
  {
    digitalWrite(led4,HIGH);
    saved[ii] = millis() - sec;
    sec= millis();
    ii++;
    flags = 1;
  }
  if (Mic.getValue() < 80)
  {
    digitalWrite(led4,LOW);
    flags = 0;
  }
  flagf = 1;
}  

void record ()
{
  
  if(Mic.getValue() > 80 && flagc == 0)
  {
    digitalWrite(led4,HIGH);
    hear[i] = millis() - sec;
    sec= millis();
    i++;
    flagc = 1;
  }
  if (Mic.getValue() < 80)
  {
    digitalWrite(led4,LOW);
    flagc = 0;
  }
}

void check ()
{ if (i == ii)
  {
    for (int j=1;j<=i;j++)
    {
      int x = hear[j];
      int y =saved[j];
      if (x+400 >= y && x-400 <=y )
      {
        counter++;
      }
    }
    if (counter == i)
    {
      digitalWrite(pin1,HIGH);
      digitalWrite(pin2,HIGH);
      digitalWrite(pin3,HIGH);
      digitalWrite(pin4,HIGH);
    }
  }
  counter = 0;
  for (int i=0; i<=20;i++)
  {
    hear[i] = 0;
  }
  i = 0; 
}