Basic Calculator with +, -, ÷, × operation support. Go through the free Standford CS193P course videos to gain some understanding about the code and auto-layout concepts.
However the Calculator example used in the videos is different from this calculator. Calculator used in the CS193P is actually a Reverse Polish Notation calculator which is somewhat advaned and hence needs a tad bit complicated code.
This is a very simple and basic calculator which should be helpful if you are a beginner with Swift or iOS development. Use of AutoLayout makes this work fine on all kinds of orientations and screen sizes.