Arduino keymatrix example

void setup() {
pinMode(rowPin1, OUTPUT);
pinMode(rowPin2, OUTPUT);
pinMode(rowPin3, OUTPUT);
pinMode(rowPin4, OUTPUT);
pinMode(colPin1, INPUT_PULLUP);
pinMode(colPin2, INPUT_PULLUP);
pinMode(colPin3, INPUT_PULLUP);
pinMode(colPin4, INPUT_PULLUP);
digitalWrite(rowPin1, HIGH);
digitalWrite(rowPin2, HIGH);
digitalWrite(rowPin3, HIGH);
digitalWrite(rowPin4, HIGH);
Serial.begin(9600);
}

void checkRow(int rowPin) {
digitalWrite(rowPin, LOW);
if(digitalRead(colPin1) == LOW) {
Serial.println("Button/switch at column 1 is pressed");
}
if(digitalRead(colPin2) == LOW) {
Serial.println("Button/switch at column 2 is pressed");
}
if(digitalRead(colPin3) == LOW) {
Serial.println("Button/switch at column 3 is pressed");
}
if(digitalRead(colPin4) == LOW) {
Serial.println("Button/switch at column 4 is pressed");
}
digitalWrite(rowPin, HIGH);
}

void loop() {
Serial.println("Checking row 1");
checkRow(rowPin1);
Serial.println("Checking row 2");
checkRow(rowPin2);
Serial.println("Checking row 3");
checkRow(rowPin3);
Serial.println("Checking row 4");
checkRow(rowPin4);
delay(200);
}