// linebot1.nqc
//    turn by stopping one tread

// sensor and motors
#define EYE    SENSOR_2
#define LEFT   OUT_A
#define RIGHT  OUT_C

// thresholds
#define TOO_DARK   38
#define TOO_BRIGHT 42

task main()
{
    SetSensor(EYE, SENSOR_LIGHT);
    On(LEFT+RIGHT);

    while(true)
    {
        if (EYE <= TOO_DARK)
        {
            Off(LEFT);
            On(RIGHT);
        }
        else if (EYE >= TOO_BRIGHT)
        {
            Off(RIGHT);
            On(LEFT);
        }
        else
        {
            On(LEFT+RIGHT);
        }
    }
}