Arithmetic Operators
1. The Five (+ shortcuts)
+ - * / % plus += -= *= /= %=. Beginners must master integer division and % (remainder) — they cause 80% mistakes.
2. Rules That Bite
| Rule | Example → Result | Why |
|---|---|---|
| int/int = int (cut!) | 7/2 → 3 (not 3.5!) |
both int → int |
| Need decimal? make one double | 7/2.0 → 3.5 |
int+double → double |
% = remainder |
7%3 → 1, 10%5 → 0 (divisible!) |
great for even/odd, last digit |
+ with String = join |
"5"+5 → "55" |
String wins |
Precedence: * / % before + - |
2+3*4 → 14 |
brackets to be safe: (2+3)*4 = 20 |
3. Code — Marks Average Done Right
public class Avg {
public static void main(String[] args) {
int a = 7, b = 2;
System.out.println(a / b); // 3 (trap! int division)
System.out.println(a / 2.0); // 3.5 (fix: .0 makes double)
System.out.println(a % b); // 1 (remainder)
int n = 123;
System.out.println(n % 10); // 3 (last digit trick!)
int x = 10;
x += 5; // x = x+5 → 15 (shortcut)
System.out.println("Total:" + x + 5); // Total:155 (left-to-right join!)
System.out.println("Total:" + (x + 5)); // Total:20 (brackets fix)
}
}
4. Traps
7/2= 3 in Java (not 3.5) — #1 beginner bug in average programs."Total:"+x+5joins left-to-right → brackets for math.%with negatives:-7%3= -1 (sign follows left).
5. Exam Points
- Predict output (
7/2,7%3,"5"+5) — 5 marks, very frequent. - Average program with correct
2.0— 3-5 marks, frequent.