Pattern Matching (C# 7+)

object o = 123;
if (o is int n && n > 100)
{
    Console.WriteLine($"Large number: {n}");
}

string Size(int x) => x switch
{
    < 0 => "neg",
    0 => "zero",
    < 10 => "small",
    _ => "big"
};

Notes

Use property and relational patterns for expressive code.
Prefer switch expressions for concise mappings.