Unary Operators

Unary Operators

1. What Unary Means (beginner)

Unary = one operand. ++, --, +, -, !, ~. Most-used: ++/-- in loops. Most-confusing: i++ vs ++i.

2. Post vs Pre (the #1 confusion)

Form	Meaning	Example (x=5)
x++ (post)	use first, then +1	y=x++; → y=5, x=6
++x (pre)	+1 first, then use	y=++x; → x=6, y=6
x-- / --x	same for minus	y=x--; → y=5, x=4
-x / +x	sign flip / no-op	-5 → -5
!	boolean NOT	!true → false
~	bitwise NOT (flips bits)	~5 → -6

3. Code — See the Difference

public class Unary {
    public static void main(String[] args) {
        int x = 5;
        System.out.println(x++); // 5 (prints, then x=6)
        System.out.println(x);   // 6
        System.out.println(++x); // 7 (first x=7, then prints)
        int i = 0;
        while (i < 3) { System.out.print(i++ + " "); } // 0 1 2 (classic loop use)
        System.out.println(!true); // false
    }
}

4. Traps

• x = x++ stays same! (post saves old, then overwrites). Never write this.
• i++ in while(i<3) prints 0 1 2 — favourite output question.
• ! only on boolean: !5 is ERROR (unlike C).

5. Exam Points

• Predict output (x++ vs ++x) — 5 marks, very frequent.
• Loop trace with i++ — 3 marks, frequent.