C# 提供了哪些控制流构造？

if (score >= 90)
    grade = "A";
else if (score >= 80)
    grade = "B";
else
    grade = "F";

// ternary and null-coalescing
string status = age >= 18 ? "adult" : "minor";
string name = input ?? "default";        // ?? — use default if input is null
name ??= "fallback";                      // ??= assign if null

// traditional switch
switch (day)
{
    case "Sat":
    case "Sun":
        type = "weekend";
        break;                            // break required (no fall-through)
    default:
        type = "weekday";
        break;
}

// switch EXPRESSION (C# 8) — concise, returns a value, with pattern matching
string type = day switch
{
    "Sat" or "Sun" => "weekend",
    _ => "weekday",                        // _ = default
};

// pattern matching in switch
string describe = obj switch
{
    int n when n > 0 => "positive int",
    string s => $"string of length {s.Length}",
    null => "null",
    _ => "other",
};

for (int i = 0; i < 10; i++) { }

foreach (var item in collection) { }      // iterate any IEnumerable

while (condition) { }
do { } while (condition);                  // runs at least once

foreach (var item in items)
{
    if (item.Skip) continue;   // next iteration
    if (item.Stop) break;       // exit loop
}
return result;                  // exit method