Changing Values 🔄

Variables can change. That's why they're called variables!

public class Main {
    public static void main(String[] args) {
        int score = 0;
        score = score + 10;
        score = score + 5;
        System.out.println("Score: " + score);
    }
}

score = score + 10 means: take what's in score, add 10, put the answer back in score. Final score: 15.

Shortcuts programmers love ⚡

🔋 A robot on a mission

public class Main {
    public static void main(String[] args) {
        int battery = 100;
        battery -= 30; // drove across the field
        battery -= 25; // lifted a block
        battery += 40; // quick recharge
        System.out.println("Battery: " + battery + "%");
    }
}

Let's trace it like a detective 🕵️: 100 → 70 → 45 → 85. It prints Battery: 85%.

💡

💡 Tracing means following the code line by line and writing down each variable's value. It's the #1 skill for predicting what code does.

🌳 Fun fact

A tree grows a new ring every year. A tree-counting program could just do age++; once for every ring it sees!