const int numRows = 4; // number of rows in the keypad
   const int numCols = 4; // number of columns
   const int debounceTime = 20; // number of milliseconds for switch to be stable
   const int ledPin = 13; 
   const char password[] = "8714"; 
   int passwordIndex = 0;
   const char keymap[numRows][numCols] = {
    { '1', '2', '3' ,'A' } ,
     { '4', '5', '6' ,'B'} ,
      { '7', '8', '9' ,'C'} ,
       { '*', '0', '#' ,'D'}
       };

       
       const int rowPins[numRows] = {11,10,9,8}; 
       const int colPins[numCols] = {5,4,3,2}; // Columns 0 through 2

       void setup()
       {
        Serial.begin(9600);
         pinMode(ledPin, OUTPUT); // Set LED pin as output
          for (int row = 0; row < numRows; row++)
           {
            pinMode(rowPins[row],INPUT); // Set row pins as input
             digitalWrite(rowPins[row],HIGH); // turn on Pull-ups
              }
               for (int column = 0; column < numCols; column++)
                {
                 pinMode(colPins[column],OUTPUT); // Set column pins as outputs
                  // for writing
                   digitalWrite(colPins[column],HIGH); // Make all columns inactive
                    }
                    }

                    void loop()
                    {
                     char key = getKey();
                      if( key != 0) { // if the character is not 0 then
                       // it's a valid key press
                        Serial.print("Got key ");
                         Serial.println(key);
                          
                           // Check if the key is part of the password
                            if (key == password[passwordIndex])
                             {
                              passwordIndex++;
                               if (passwordIndex == strlen(password))
                                {
                                 Serial.println("Password correct! Turning on LED.");
                                  digitalWrite(ledPin, HIGH); 
                                   passwordIndex = 0; 
                                    }
                                     }
                                      else
                                       {
                                        passwordIndex = 0; 
                                         }
                                          
                                    
                                            if (key == 'C')
                                             {
                                              Serial.println("Turning off LED.");
                                               digitalWrite(ledPin, LOW); 
                                                }
                                                 }
                                                 }

                                          
                                                 char getKey()
                                                 {
                                                  char key = 0;
                                                   for(int column = 0; column < numCols; column++)
                                                    {
                                                     digitalWrite(colPins[column],LOW); // Activate the current column.
                                                      for(int row = 0; row < numRows; row++) // Scan all rows for
                                                       // a key press.
                                                        {
                                                         if(digitalRead(rowPins[row]) == LOW) // Is a key pressed?
                                                          {
                                                           delay(debounceTime); // debounce
                                                            while(digitalRead(rowPins[row]) == LOW);    // wait for key to be released
                                                             key = keymap[row][column];     // Remember which key
                                                              // was pressed.
                                                               }
                                                                }
                                                                 digitalWrite(colPins[column],HIGH); // De-activate the current column.
                                                                  }
                                                                   return key; // returns the key pressed or 0 if none
                                                                   }