Dictionaries and LINQ

A Dictionary<string, int> maps each key to a value. After var gold = new Dictionary<string, int>();, the line gold["Layan"] = 50; adds the key if it isn't there yet, or replaces its value if it is. Reading a key that doesn't exist, however, throws a KeyNotFoundException, which is why the program stops at gold["Sara"]++ the first time. So check first with ContainsKey, or use TryGetValue(key, out int value), which returns whether the key was found and puts its value in value, or zero if it wasn't. It's the same Try pattern you saw in the lesson on methods.

LINQ, from System.Linq, gives you ready-made methods for asking questions of any collection, and most of them take a short function written with an arrow, called a lambda. Where(x => x > 10) keeps the items that meet the condition, Select(x => x * 2) transforms each item, OrderBy sorts in ascending order and OrderByDescending in descending order, Sum() adds everything up, and Count(x => ...) counts the items that meet the condition. You can chain them like this: scores.Where(s => s >= 50).OrderBy(s => s).ToList().

A dictionary is a collection of pairs, each with a Key and a Value, so LINQ works on it just as it does on a list, and Values gives you just its values. Keep in mind that a query doesn't run when you write it but when you go through its result, so if the collection changes in between, the result changes too. ToList() runs it right away and stores the result in a list.