Robot Math (With Surprises!) 🧮

Java does math with +, -, * (times) and / (divide):

public class Main {
    public static void main(String[] args) {
        int rows = 6;
        int seedsPerRow = 8;
        System.out.println("Seeds to plant: " + rows * seedsPerRow);
    }
}

😮 Surprise #1: whole-number division

When you divide two ints, Java throws away the decimal part:

public class Main {
    public static void main(String[] args) {
        System.out.println(7 / 2);   // prints 3, not 3.5!
        System.out.println(7.0 / 2); // prints 3.5
    }
}

If you want decimals, use at least one double (like 7.0).

🥚 The remainder operator %

% gives the remainder: what's left over after dividing.

A farmer collects 17 eggs and packs them in cartons of 6:

public class Main {
    public static void main(String[] args) {
        int eggs = 17;
        System.out.println("Full cartons: " + eggs / 6);
        System.out.println("Eggs left over: " + eggs % 6);
    }
}

That prints Full cartons: 2 and Eggs left over: 5. 🥚

💡

🧠 Trick: number % 2 is 0 for even numbers and 1 for odd numbers. Robots use this to do something every other time!

😮 Surprise #2: + with text and numbers

+ adds numbers, but glues text. Java works left to right:

public class Main {
    public static void main(String[] args) {
        System.out.println("Total: " + 2 + 3);   // Total: 23
        System.out.println("Total: " + (2 + 3)); // Total: 5
    }
}

Brackets make Java do the math first.

🌱 Fun fact

Some farms use robots that plant seeds in perfectly straight rows and count every one, the same kind of math you just did!