byte h=0,v=0;              // variables used in for loops
const int period=50;       // A little delay to avoid errors.
int kdelay=0;              // Non Blocking Delay
const byte rows=4;         // Rows in Keypad
const byte columns=4;      // Columns in Keypad
const byte Output[rows]={6,7,8,9};   //Row connceted to Arduino Pins
const byte Input[columns]={2,3,4,5}; //Columns connected to Arduino Pins
const int Led1=10;
const int Led2=11;
const int Led3=12;
const int Led4=13;
const int Led5=14;
const int Led6=15;
const int Led7=16;
const int Led8=17;
const int Led9=18;

void setup()
{
  for(byte i=0;i<rows;i++)      //Loop to declare output pins.
  {
  pinMode(Output[i],OUTPUT);
  }
  for(byte s=0;s<columns;s++)  // Loop to decalre Input pins, Initial Pulledup.
  {
    pinMode(Input[s],INPUT_PULLUP);
  }
  Serial.begin(9600);         // Initializing Serail communication.
}
void loop()
{
  if(millis()-kdelay>period) //used to make non-blocking delay
  {
    kdelay=millis();  //capture time from millis function
switch (keypad())     //Switch to get which button is pressed.
   {
            case 0:
            Serial.println(1);
            digitalWrite(Led1, HIGH);
            delay(100);
            digitalWrite(Led1, LOW);
       break;
            case 1:
            Serial.println(2);
            digitalWrite(Led2, HIGH);
            delay(100);
            digitalWrite(Led2, LOW);
       break;
            case 2:
            Serial.println(3);
            digitalWrite(Led3, HIGH);
            delay(100);
            digitalWrite(Led3, LOW);
       break;
            case 3:
            Serial.println("A");
            digitalWrite(Led1, HIGH);
            digitalWrite(Led2, HIGH);
            digitalWrite(Led3, HIGH);
       break;
            case 4:
            Serial.println(4);
            digitalWrite(Led4, HIGH);
            delay(100);
            digitalWrite(Led4, LOW);
       break;
            case 5:
            Serial.println(5);
            digitalWrite(Led5, HIGH);
            delay(100);
            digitalWrite(Led5, LOW);
       break;
            case 6:
            Serial.println(6);
            digitalWrite(Led6, HIGH);
            delay(100);
            digitalWrite(Led6, LOW);
       break;
            case 7:
            Serial.println("B");
            digitalWrite(Led4, HIGH);
            digitalWrite(Led5, HIGH);
            digitalWrite(Led6, HIGH);
       break;
            case 8:
            Serial.println(7);
            digitalWrite(Led7, HIGH);
            delay(100);
            digitalWrite(Led7, LOW);
       break;
            case 9:
            Serial.println(8);
            digitalWrite(Led8, HIGH);
            delay(100);
            digitalWrite(Led8, LOW);
       break;
            case 10:
            Serial.println(9);
            digitalWrite(Led9, HIGH);
            delay(100);
            digitalWrite(Led9, LOW);
       break;
            case 11:
            Serial.println("C");
            digitalWrite(Led7, HIGH);
            digitalWrite(Led8, HIGH);
            digitalWrite(Led9, HIGH);
       break;
            case 12:
            Serial.println("*");
            digitalWrite(Led1, HIGH);
            digitalWrite(Led4, HIGH);
            digitalWrite(Led7, HIGH);

       break;
            case 13:
            Serial.println(0);
            digitalWrite(Led2, HIGH);
            digitalWrite(Led5, HIGH);
            digitalWrite(Led8, HIGH);
       break;
            case 14:
            Serial.println("#");
       break;
            case 15:
            Serial.println("D");
            digitalWrite(Led1, LOW);
            digitalWrite(Led2, LOW);
            digitalWrite(Led3, LOW);
            digitalWrite(Led4, LOW);
            digitalWrite(Led5, LOW);
            digitalWrite(Led6, LOW);
            digitalWrite(Led7, LOW);
            digitalWrite(Led8, LOW);
            digitalWrite(Led9, LOW);
       break;
            default:
            ;
}
}
}

// Below function is used to detect which button is pressed.

byte keypad()
{
 static bool no_press_flag=0;
  for(byte x=0;x<columns;x++)
  {
     if (digitalRead(Input[x])==HIGH);
     else
     break;
     if(x==(columns-1))
     {
      no_press_flag=1;
      h=0;
      v=0;
     }
  }
  if(no_press_flag==1)
  {
    for(byte r=0;r<rows;r++)
    digitalWrite(Output[r],LOW);
    for(h=0;h<columns;h++)
    {
      if(digitalRead(Input[h])==HIGH)
      continue;
      else
      {
          for (v=0;v<rows;v++)
          {
          digitalWrite(Output[v],HIGH);
          if(digitalRead(Input[h])==HIGH)
          {
            no_press_flag=0;
            for(byte w=0;w<rows;w++)
            digitalWrite(Output[w],LOW);
            return v*4+h;
          }
          }
      }
    }
  }
 return 50;
}