Articles

Concepts and traps, explained with runnable evidence. If a claim below can be shown in six lines of code, it is.

Language core

Why is 7 / 2 = 3 in C#? Integer division explained
Both operands int → fraction discarded, toward zero. The three fixes, the negative-number rules, and when it is exactly what you want.
var vs explicit types — when each is right
var is compile-time inference, not dynamic typing. Where it helps, where it hides load-bearing information.
struct vs class — value vs reference semantics
Assignment copies a struct, aliases a class. The mutation test that makes it click, the gotcha it explains, and when to pick which.
== vs .Equals() — which one, when
They agree for primitives; they split on null handling and on what "equal" means. Case-insensitive compare done right.
string vs StringBuilder — immutability and the += trap
Why s.Replace() changes nothing, why += in a loop is O(n²), and the three-piece rule: interpolate, Join, or StringBuilder.
const vs readonly vs static readonly — three kinds of "never changes"
Compile-time literal vs per-object vs per-class. Why const copies into call sites, and why readonly doesn't freeze contents.
ref vs out vs in — what each parameter mode does
out writes only, ref reads and writes, in reads without copying. The direction table plus the CS0165/CS1510/CS0177 rules.
abstract class vs interface — the real difference
Half-built family member with state vs pure promise any class can make. Why one base class but many interfaces.