int r1 = 2;    //row pins
int r2 = 3;
int c1 = 4;    //collumn pins
int c2 = 5;

void setup() {
  // put your setup code here, to run once:
pinMode(r1, OUTPUT);
pinMode(r2, OUTPUT);
pinMode(c1, INPUT_PULLUP);
pinMode(c2, INPUT_PULLUP);
}

void loop() {
  // put your main code here, to run repeatedly:
digitalWrite(r1, HIGH);
if(digitalRead(c1)){
} 
else{Serial.print("4");}

if(digitalRead(c2)){
}
else{Serial.print("3");}
digitalWrite(r1, LOW);

digitalWrite(r2, HIGH);
if(digitalRead(c1)){
} 
else{Serial.print("2");}

if(digitalRead(c2)){
}
else{Serial.print("1");}
digitalWrite(r2, LOW);
}