const int numRows=4;
const int numCols=4;
const int debounceTime=20;
const char keymap[numRows][numCols]={
  {'1','2','3','+'},
  {'4','5','6','-'},
  {'7','8','9','x'},
  {'*','0','#','/'}
};
const int rowPins[numRows]={7,6,5,4};
const int colPins[numCols]={11,10,9,8};
void setup()
{
  Serial.begin(9600);
  for(int row=0;row<numRows;row++)
  {
    pinMode(rowPins[row],INPUT);
    digitalWrite(rowPins[row],HIGH);
  }
  for(int cloumn=0;cloumn<numCols;cloumn++)
  {
    pinMode(colPins[cloumn],OUTPUT);
    digitalWrite(colPins[cloumn],HIGH);
  }
}

void loop() 
{
  char key=getkey();
  if(key!=0)
  {
    Serial.print("Got key");
    Serial.println(key);
  }
}
char getkey()
{
  char key=0;
  for(int cloumn=0;cloumn<numCols;cloumn++)
  {
    digitalWrite(colPins[cloumn],LOW);
  
  for(int row=0;row<numRows;row++)
  {
    if(digitalRead(rowPins[row])==LOW)
    {
      delay(debounceTime);
      while(digitalRead(rowPins[row])==LOW);
      key=keymap[row][cloumn];
     }
   }
  digitalWrite(colPins[cloumn],HIGH);
  }
 return key;
}