DAY 3 — Structs and Modeling Data (One Concept at a Time)

Goal (End of Day 3)

• Understand what a struct is
• Create and use structs
• Pass structs to functions
• Understand value vs pointer usage at a basic level
• Model simple real-world data in Go

1. What a Struct Is

Concept

• A struct groups related values under one name

Example type Person struct { Name string Age int }

Rules

• Fields have names and types
• Field order matters for readability, not access
• Structs define shape, not behavior

Exercise

• Define a struct representing a Book (title, author, pages)

2. Creating and Using Struct Values

Concepts

• Struct literals
• Accessing fields with dot notation

Example p := Person{Name: "Alice", Age: 30} fmt.Println(p.Name)

Rules

• Field names must match the struct definition
• Unspecified fields get zero values

Exercise

• Create a Book value and print its fields

3. Passing Structs to Functions

Concepts

• Structs can be passed like any other value
• Functions can return structs

Example func printPerson(p Person) { fmt.Println(p.Name, p.Age) }

Exercise

• Write a function that takes a Book and returns a formatted string

4. Pointers to Structs (Intro Only)

Concepts

• Using *T to avoid copying large structs
• Modifying struct fields via pointers

Example func birthday(p *Person) { p.Age += 1 }

Rules

• Use pointers when a function needs to modify the struct
• Go handles pointer dereferencing automatically for structs

Exercise

• Write a function that increments the page count of a Book

5. Mini Program (Mandatory)

Program: Library Item

Requirements

• Define a struct for an item (ID, Name, Count)
• Create a slice of items
• Write a function that updates Count by ID
• Handle missing ID with an error

Exit Criteria (Must All Be True)

• Defined at least one struct
• Created struct values correctly
• Passed structs to functions
• Used a pointer to modify a struct
• Program compiles and runs cleanly

Day 4 Preview

• Methods on structs
• Value vs pointer receivers
• Attaching behavior to data