Reading an analog voltage

app.ino

void setup()
{
    // Initialise my serial port with 9600 baud
    Serial.begin(9600);
}

void loop()
{
    // Analog values are read as integer values between 1 and 1023.
    // Each 1 is a fraction of 5V. So 0 = 0V, 1023 = 5V, and the scale 
    // goes in-between. 
    const float VOLTAGE_MULTIPLIER = (5.0 / 1023.0);

    // Read the analog value on pin A0 (as fractions of 5V).
    int sensorValue = analogRead(A0);

    // Convert to volts using our multiplier.
    float sensorVoltage = sensorValue * VOLTAGE_MULTIPLIER;
    
    // Write the current voltage to the Serial port.
    Serial.println(sensorVoltage);
}