Chapter 1 · Foundations

Variables and arithmetic

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Step 1 of 22 · Concept

A variable is a named box

Lesson 2 showed main's frame with boxes in it. A variable is one of those boxes, with a name you choose.

int age = 15;
partmeans
intthe type: what the box can hold
agethe name of the box
= 15the value put in the box

In this lesson you will fill boxes, change them and calculate with them.

public class Area {
    public static void main(String[] args) {
        int width = 7;
        int height = 6;
        int area = width * height;
        System.out.println("Area: " + area);
    }
}

public class Fruit {
    public static void main(String[] args) {
        int apples = 2;
        int pears = 3;
        System.out.println("Fruit: " + apples + pears);
    }
}

public class Birthday {
    public static void main(String[] args) {
        int age = 17;
        boolean adult = age >= 18;
        System.out.println("Age " + age + ", adult: " + adult);

        age = age + 1;
        adult = age >= 18;
        System.out.println("Age " + age + ", adult: " + adult);

        age += 10;
        System.out.println("Ten years later: " + age);
    }
}

public class Receipt {
    public static void main(String[] args) {
        // declare the item, the count and the price

        // print the total and whether delivery is free

        // add 2 to the count, then print both lines again
    }
}

public class Divide {
    public static void main(String[] args) {
        System.out.println(7 / 2);
        System.out.println(7 / 2.0);
        System.out.println(7 % 2);
    }
}

public class Average {
    public static void main(String[] args) {
        int a = 4;
        int b = 7;
        int c = 9;
        double average = (a + b + c) / 3;
        System.out.println("Average: " + average);
    }
}

public class Game {
    public static void main(String[] args) {
        // her name, her points (0 to start), the levels

        // she scores 40 points: print the first line

        // she scores 35 more: print the second line

        // the points per level, and whether she won
    }
}

public class Swap {
    public static void main(String[] args) {
        int a = 3;
        int b = 8;
        // swap the values of a and b
        System.out.println("a = " + a + ", b = " + b);
    }
}
Terminal
Step 1 of 8Width times height

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