Code concepts are designed to show you how code works in a very simple fashion. They may not include both inputs and outputs, but running these programs should give you an idea of how the building blocks of many programs work. 

Do Nothing

Blink

Blink Alternating LEDs

Dim with Blink

Fade

LED Counter

Serial Control Blink

Alternate Blinking LEDs with millis()

For Loop

While Loop 

If Statement

Switch Case Statement