Basic Arduino Multiplexer code

multiplex-read.c

/* 
 *  Reading switches and tell to Serial.
 *
 */
 
int numPins = 2;
int out[] = {4,5};
int in[] = {2,3};


void setup(){
   // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
  Serial.println("Initializing!");
  Serial.println("Pins: ");

  // make the pushbutton's pin an input:
  for (int i=0; i < numPins; i++){
    pinMode(in[i], INPUT);
    pinMode(out[i], OUTPUT);
    Serial.print("{");
    Serial.print(in[i]);
    Serial.print(" ");
    Serial.print(out[i]);
    Serial.println("}");
  }
    delay(100);
}

 
void loop(){

   checkSwitch();
   delay(10);
  
}


int checkSwitch(){  
 
  int val, row, column = 0;
  
  for(int i =0; i<numPins; i++){
      digitalWrite(out[i], LOW);
  }
  
  
  for(int i=0; i<numPins; i++){
    row = i;
    // get the row
    digitalWrite(out[i], HIGH);
    for(int j=0; j<numPins; j++){
     
      val = digitalRead(in[j]);
      if (val == HIGH){
        column = j;
        break;
      }
    }    
    if (column > 0){
       break;
    } 
    digitalWrite(out[i], LOW);
  }
  if (column > 0){
    Serial.print("Pushed: {");
    Serial.print(row);
    Serial.print(" ");
    Serial.print(column);
    Serial.println("}");
  }
  return 1;
}