Variables and types

C# is statically typed. Web apps use value types (int, bool, DateTime), reference types (string, classes), and generics (List<Product>) everywhere—from route IDs to JSON payloads.

Common types in ASP.NET

• int, long — primary keys, counts, pagination
• string / string? — names, slugs, optional query params
• DateTime / DateTimeOffset — timestamps (prefer UTC in APIs)
• decimal — money (avoid float for currency)
• Guid — opaque IDs in distributed systems

var and target-typed new

var users = new List<User>();
User dto = new() { Name = "Ada" };

var is compile-time inferred—not dynamic. Use when the type is obvious from the right-hand side.

Important interview questions and answers

1. Q: Value type vs reference type?
   A: Value types copy on assignment (stack or inline); reference types share heap objects—mutations visible through all references.
2. Q: string? in nullable context?
   A: Compiler warns if you dereference without null check—reduces NullReferenceException in production.

Self-check

1. Which type is safer for prices: decimal or double?
2. Does var mean dynamic typing?