Dictionary... No Index Needed!

- Dictionary has keys and values, no index. How about array?

- Values are not in any particular order

- A key has to be unique.

- They are UNORDERED

- Keys in dictionary must be same type, but does not need to match type of value

- Keys and values are same type: var usStates = ["CA": "California", "TX": "Texas", "WA": "Washington"]

- Keys are doubles and values are strings: let fraction = [0.25: "1/4", 0.5: "1/2", 1: "1"]

- You are given optional when accessing in dictionary. Why? Remember nil or an item does not exist.

- You need to unwrap the value before you can use in dictionary.

- Use if-let to check if the value is a nil

- Add value to dictionary usStates["CA"] = nil