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Shorthand for updating

• Updating a variable from itself is so common it has shorthand.
• A compound assignment operator 复合赋值运算符 combines an operation with =.
• x += 3; means exactly x = x + 3;.
• The family: +=, -=, *=, /=, %=.

The five operators

• x += 5 → add 5 to x. x -= 5 → subtract 5.
• x *= 2 → double x. x /= 2 → halve x (int rules apply).
• x %= 3 → replace x with x % 3 (the remainder).
• Each reads the current value, applies the op, and stores the result back.

Compound assignment operators traced on one variable

Increment and decrement

• x++ adds 1 to x (same as x += 1 or x = x + 1).
• x-- subtracts 1 from x.
• These are extremely common in loops to step a counter.
• They change the variable in place — no = needed.

Same type rules apply

• Compound operators obey the same type rules as the long form.
• int x = 7; x /= 2; gives 3 (int division still truncates).
• x += 2.5; on an int would need care — the type of x doesn't change.
• The shorthand is only shorter; the arithmetic is identical.