C# Cheatsheet

// ── Basics (top-level statements) ───────
int x = 42;
double pi = 3.14;
string name = "Ada";
var list = new List<string>();       // inference
Console.WriteLine($"{name} is {x}"); // interpolation

// ── Control flow ────────────────────────
if (x > 10) { } else if (x > 5) { } else { }
for (int i = 0; i < 5; i++) { }
foreach (var item in items) { }
while (cond) { }
var label = x > 10 ? "big" : "small";
value ?? fallback;  obj?.Prop;       // null tools

// switch expression + patterns:
string Describe(object o) => o switch {
    int n when n > 100 => "big number",
    int n              => $"number {n}",
    string s           => $"text {s.Length} long",
    null               => "nothing",
    _                  => "unknown",
};

// ── Records & classes ───────────────────
record Point(int X, int Y);          // value equality free
var p2 = p1 with { Y = 5 };          // non-destructive update

class Dog {
    public string Name { get; init; }        // properties
    public int Age { get; private set; }
    public string Bark() => $"{Name} woofs"; // expression body
}

// ── Collections ─────────────────────────
var nums = new List<int> { 3, 1, 4 };
nums.Add(1); nums[0]; nums.Count; nums.Contains(4);
var ages = new Dictionary<string, int> { ["Ada"] = 17 };
ages.TryGetValue("Eve", out var age);
int[] arr = [1, 2, 3];               // collection expression

// ── LINQ — the crown jewel ──────────────
var honorRoll = students
    .Where(s => s.Grade >= 90)
    .OrderBy(s => s.Name)
    .Select(s => s.Name)
    .ToList();
var total = nums.Sum();
var best = students.MaxBy(s => s.Grade);
var byAge = students.GroupBy(s => s.Age);
var any = students.Any(s => s.Grade == 100);

// ── Async ───────────────────────────────
async Task<string> FetchAsync(string url) {
    using var http = new HttpClient();
    return await http.GetStringAsync(url);
}
var results = await Task.WhenAll(a, b);   // concurrent

// ── Exceptions ──────────────────────────
try { Risky(); }
catch (IOException e) { Handle(e); }
finally { Cleanup(); }

// dotnet new console | dotnet run | dotnet test
// dotnet add package Newtonsoft.Json