Exercises

These exercises close the chapter on structs, enums, and unions. They are meant to make the data model concrete.

Exercise 7-29

Define a struct named Point with two fields:

x: i32
y: i32

Create a value with x = 3 and y = 4, then print both fields.

Exercise 7-30

Add a method named move to Point.

It should take a pointer to Point and two numbers, dx and dy. It should add dx to x and dy to y.

Expected use:

var p = Point{
    .x = 3,
    .y = 4,
};

p.move(10, -2);

After the call, p.x should be 13 and p.y should be 2.

Exercise 7-31

Define a struct named Rectangle.

const Rectangle = struct {
    width: u32,
    height: u32,

    // add area here
};

Add a method named area that returns width * height.

Exercise 7-32

Define an enum named Direction.

It should have four values:

north
south
east
west

Write a function:

fn isVertical(d: Direction) bool

It should return true for north and south, and false for east and west.

Exercise 7-33

Define an enum named LogLevel.

const LogLevel = enum {
    debug,
    info,
    warn,
    err,
};

Write a function:

fn levelName(level: LogLevel) []const u8

It should return "debug", "info", "warn", or "err".

Use a switch.

Exercise 7-34

Define a tagged union named Value.

It should have these variants:

integer: i64
boolean: bool
text: []const u8

Create one value of each variant.

Write a function:

fn printValue(value: Value) void

It should switch on the value and print the payload.

Exercise 7-35

Define a tagged union named Shape.

It should have two variants:

circle: Circle
rectangle: Rectangle

where:

const Circle = struct {
    radius: f64,
};

const Rectangle = struct {
    width: f64,
    height: f64,
};

Write a function:

fn area(shape: Shape) f64

For a circle, return 3.141592653589793 * radius * radius.

For a rectangle, return width * height.

Exercise 7-36

Define a packed struct named Permissions.

It should contain three boolean fields:

read: bool
write: bool
execute: bool

Create this value:

const p = Permissions{
    .read = true,
    .write = false,
    .execute = true,
};

Print each field.

Exercise 7-37

Define a packed struct named ByteParts.

It should contain:

low: u4
high: u4

Convert a u8 value to ByteParts with @bitCast, then print low and high.

Example input:

const raw: u8 = 0xab;

Exercise 7-38

Use @sizeOf and @alignOf on these types:

u8
u16
u32
u64

Print the result for each type.

Then define this struct:

const Example = struct {
    a: u8,
    b: u32,
};

Print its size and alignment.

Exercise 7-39

Change the order of the fields:

const Example = struct {
    b: u32,
    a: u8,
};

Print its size and alignment again. Compare the result.

Exercise 7-40

Write three versions of a small data type:

const Normal = struct {
    a: u8,
    b: u32,
};

const External = extern struct {
    a: u8,
    b: u32,
};

const Packed = packed struct {
    a: u8,
    b: u32,
};

Print the size and alignment of each.

Explain in a comment when each form should be used.