I am new to Arduino. I am learning from Arduino Cookbook. I was using tinkercad.com for running my Arduino code. But it is not working. Please look into this:

const char keymap[4][4]={
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
 };
const int rpin[]={9,8,7,6};
const int cpin[]={5,4,3,2};
void setup()
{
  Serial.begin(9600);
  for(int i=0;i<4;i++)
  {
    pinMode(rpin[i],INPUT);
    digitalWrite(rpin[i],HIGH);
  }
  for(int j=0;j<4;j++)
  {
    pinMode(cpin[j],INPUT);
    digitalWrite(cpin[j],HIGH);
  }
}
void loop()
{
  char key=getkey();
  if(key!=0)
  {
   Serial.println(key); 
  }  
}
char getkey()
{
  char key=0;
  for(int i=0;i<4;i++)
  {
    digitalWrite(rpin[i],LOW);
    for(int j=0;j<4;j++)
    {
      if (digitalRead(cpin[j])==LOW)
      key=keymap[i][j];
    }
    digitalWrite(rpin[i],HIGH);
  }
  return key;
}

and the connection pic: