Operators and expressions

Arithmetic and its surprises

+ - * / % on numbers. You know 7 / 2 == 3 (integer division truncates). The % remainder operator completes the toolkit: n % 2 == 0 reads "n is even", minutes % 60 is "minutes past the hour". Watch sign behavior: -7 % 2 is -1 in C# — the remainder takes the dividend's sign.

Compound assignment += -= *= /= updates in place: total += price is total = total + price. ++/-- add or subtract one; prefer i += 1 style clarity in expressions, keep ++ for loops.

Comparison operators

== != < > <= >= produce bool. On numeric types they compare values. On string, == compares contents. On most classes, == compares references — two different objects with equal fields are not ==. (You'll meet records in Module 13, which fix this for data types.)

Logic and short-circuiting

&& (and), || (or), ! (not) combine bools — and they short-circuit:

if (count > 0 && total / count > 10) { ... }   // safe: division only when count > 0
if (name != null && name.Length > 0) { ... }   // safe: dereference only after null check

The right side of && runs only when the left side was true; the right side of || only when the left was false. This is not an optimization nicety — it's how you write guarded checks. & and | (single) exist but always evaluate both sides; you want &&/|| for control flow.

Precedence: ! binds tightest, then arithmetic, then comparisons, then &&, then ||. When in doubt, parenthesize — a && b || c is (a && b) || c, but nobody should have to remember that.