Accessing struct fields in Go - Mini Project: Build & Apply

Accessing struct fields

📖 Scenario: You are creating a simple program to store information about a book in a library.

🎯 Goal: You will create a struct to hold book details, set up a book variable, and then access and print its fields.

📋 What You'll Learn

Create a struct type named Book with fields Title (string) and Pages (int).

Create a variable myBook of type Book with Title set to "Go Programming" and Pages set to 300.

Access the Title and Pages fields of myBook and store them in variables bookTitle and bookPages.

Print the values of bookTitle and bookPages.

💡 Why This Matters

🌍 Real World

Structs are used to group related data together, like storing information about books, people, or products in programs.

💼 Career

Understanding structs and how to access their fields is essential for Go programming jobs, especially when working with data models and APIs.

1

Create the Book struct

Create a struct type called Book with two fields: Title of type string and Pages of type int.

Go

// Define the Book struct with Title and Pages fields
// Your code here

Hint

Use type Book struct {} syntax to define the struct with the two fields inside.

2

Create a Book variable

Inside the main function, create a variable called myBook of type Book and set Title to "Go Programming" and Pages to 300.

Go

package main

type Book struct {
    Title string
    Pages int
}

func main() {
    // Create myBook with Title "Go Programming" and Pages 300
    // Your code here
}

Hint

Use struct literal syntax: myBook := Book{Title: "Go Programming", Pages: 300}.

3

Access struct fields

Inside the main function, after creating myBook, create two variables: bookTitle and bookPages. Assign myBook.Title to bookTitle and myBook.Pages to bookPages.

Go

package main

type Book struct {
    Title string
    Pages int
}

func main() {
    myBook := Book{
        Title: "Go Programming",
        Pages: 300,
    }
    // Assign myBook.Title to bookTitle and myBook.Pages to bookPages
    // Your code here
}

Hint

Use dot notation to access fields: myBook.Title and myBook.Pages.

4

Print the field values

Use fmt.Println to print the values of bookTitle and bookPages inside the main function.

Go

package main

import "fmt"

type Book struct {
    Title string
    Pages int
}

func main() {
    myBook := Book{
        Title: "Go Programming",
        Pages: 300,
    }
    bookTitle := myBook.Title
    bookPages := myBook.Pages
    // Print bookTitle and bookPages
    // Your code here
}

Hint

Use fmt.Println(bookTitle) and fmt.Println(bookPages) to print the values on separate lines.

Practice

1.

Which of the following is the correct way to access the Age field of a struct variable person in Go?

easy

A. person.Age()

B. person->Age

C. person["Age"]

D. person.Age

Solution

1. Step 1: Understand struct field access syntax in Go

   In Go, struct fields are accessed using dot notation: structVariable.fieldName.

2. Step 2: Apply to the given variable and field

   For variable person and field Age, the correct access is person.Age.

3. Final Answer:

   person.Age -> Option D

4. Quick Check:

   Use dot notation for struct fields = person.Age [OK]

Hint: Use dot (.) to access struct fields in Go [OK]

Common Mistakes:

• Using arrow (->) like in C/C++
• Trying to access fields like map keys
• Calling field as a function with ()

2.

Which of the following code snippets correctly accesses the Title field of a struct book?

type Book struct {
    Title string
    Author string
}

var book Book
// Access Title here

easy

A. book.Title

B. book->Title

C. book["Title"]

D. book.Title()

Solution

1. Step 1: Recall Go struct field access syntax

   Fields in Go structs are accessed using dot notation without parentheses or brackets.

2. Step 2: Apply to the book variable and Title field

   The correct syntax is book.Title.

3. Final Answer:

   book.Title -> Option A

4. Quick Check:

   Dot notation accesses struct fields = book.Title [OK]

Hint: Remember: struct fields use dot, not brackets or arrows [OK]

Common Mistakes:

• Using brackets like a map
• Using arrow operator (->)
• Calling field as a method

3.

What will be the output of the following Go program?

package main
import "fmt"

type Person struct {
    Name string
    Age  int
}

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

medium

A. Alice

B. 30

C. Name

D. Compilation error

Solution

1. Step 1: Understand struct initialization and field access

   The struct Person is initialized with Name: "Alice" and Age: 30. The variable p holds this struct.

2. Step 2: Identify the printed field

   The code prints p.Age, which is 30.

3. Final Answer:

   30 -> Option B

4. Quick Check:

   Print struct field Age = 30 [OK]

Hint: Print struct.field to get that field's value [OK]

Common Mistakes:

• Printing the Name field instead of Age
• Expecting field name as output
• Thinking code causes error

4.

Identify the error in the following Go code and choose the correct fix:

package main
import "fmt"

type Car struct {
    Model string
    Year  int
}

func main() {
    c := Car{Model: "Tesla", Year: 2022}
    fmt.Println(c->Model)
}

medium

A. Add parentheses: c.Model()

B. Change c->Model to c["Model"]

C. Change c->Model to c.Model

D. No error, code is correct

Solution

1. Step 1: Identify incorrect field access operator

   The code uses c->Model, which is invalid in Go. Go uses dot notation for struct fields.

2. Step 2: Correct the field access syntax

   Replace c->Model with c.Model to fix the error.

3. Final Answer:

   Change c->Model to c.Model -> Option C

4. Quick Check:

   Use dot (.) not arrow (->) for struct fields [OK]

Hint: Use dot (.) for struct fields, not arrow (->) [OK]

Common Mistakes:

• Using arrow operator like in C/C++
• Trying to access fields like map keys
• Calling field as a function

5.

Given the struct and code below, what will be the output?

package main
import "fmt"

type Employee struct {
    ID    int
    Name  string
    Title string
}

func main() {
    e := Employee{ID: 101, Name: "Bob", Title: "Developer"}
    e.Title = "Senior Developer"
    fmt.Println(e.Title)
}

hard

A. Senior Developer

B. Developer

C. Title

D. Compilation error

Solution

1. Step 1: Understand struct field update

   The struct Employee is created with Title: "Developer". Then the field Title is updated to "Senior Developer".

2. Step 2: Identify printed value

   The code prints e.Title after update, so output is Senior Developer.

3. Final Answer:

   Senior Developer -> Option A

4. Quick Check:

   Updated struct field prints new value [OK]

Hint: Assign new value with dot, then print updated field [OK]

Common Mistakes:

• Expecting original value instead of updated
• Thinking field cannot be changed
• Confusing field name with value