byte h = 0, v = 0; //vars for for loops
const byte rows = 2; //number of rows
const byte cols = 5; //number of cols
const byte Output[rows] = {21, 20}; //pins
const byte Input[cols] = {19, 18, 16, 17, 15}; //pins
int led1 = 7;
int led2 = 8;
int led3 = 23;
int led4 = 12;

byte keypad() { //detects button presses
  static bool no_press_flag = 0; //static flag ensures nothing was press
  for (byte x = 0; x < cols; x++) { //for loop reads every button
    if (digitalRead(Input[x]) == HIGH); //read every input if high, continue. if else, break
    else
      break;
    if (x == (cols - 1)) { //if no button is pressed, flag as no button pressed
      no_press_flag = 1;
      h = 0;
      v = 0;
    }
  }
  if (no_press_flag == 1) { //if no button is pressed
    for (byte r = 0; r < rows; r++) //for loop used to make all output as low
      digitalWrite(Output[r], LOW);
    for (h = 0; h < cols; h++) { // for loop to check if one of inputs is low
      if (digitalRead(Input[h]) == HIGH) //if specific input is remain high (no press on it) continue
        continue;
      else {   //if one of inputs is low
        for (v = 0; v < rows; v++) { //for loop used to specify the number of row
          digitalWrite(Output[v], HIGH);  //make specified output as HIGH
          if (digitalRead(Input[h]) == HIGH) { //if the input that selected from first sor loop is change to high
            no_press_flag = 0;              //reset the no press flag;
            for (byte w = 0; w < rows; w++) // make all outputs as low
              digitalWrite(Output[w], LOW);
            return v * 5 + h; //return number of button
          }
        }
      }
    }
  }
  return 50;
}

void setup() {
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(led3, OUTPUT);
  pinMode(led4, OUTPUT);
  for (byte i = 0; i < rows; i++) { // for loop used to make pin mode of outputs as output
    pinMode(Output[i], OUTPUT);
  }
  for (byte s = 0; s < cols; s++) { //for loop used to make pin mode of inputs as input
    pinMode(Input[s], INPUT_PULLUP);
  }
  Serial.begin(9600);
}

void getKey() {
  switch (keypad()) {
    case 0:
      digitalWrite(led1, HIGH);
      break;
    case 1:
      digitalWrite(led2, HIGH);
      break;
    case 2:
      digitalWrite(led3, HIGH);
      break;
    case 3:
      digitalWrite(led3, HIGH);
      break;
    case 4:
      digitalWrite(led1, HIGH);
      digitalWrite(led3, HIGH);
      break;
    case 5:
      digitalWrite(led1, HIGH);
      break;
    case 6:
      digitalWrite(led2, HIGH);
      break;
    case 7:
      digitalWrite(led3, HIGH);
      break;
    case 8:
      digitalWrite(led4, HIGH);
      break;
    case 9:
      digitalWrite(led2, HIGH);
      digitalWrite(led4, HIGH);
      break;
    default:
      digitalWrite(led1, LOW);
      digitalWrite(led2, LOW);
      digitalWrite(led3, LOW);
      digitalWrite(led4, LOW);
      break;
  }
}
void loop() {
  getKey();
}