Defining structs in Go - Mini Project: Build & Apply

Defining structs

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

🎯 Goal: You will define a struct to represent a book with its title and author, then create an instance of this struct and display its details.

📋 What You'll Learn

Define a struct named Book with two fields: Title and Author, both of type string.

Create a variable named myBook of type Book with the title "The Go Programming Language" and author "Alan A. A. Donovan".

Print the book's title and author in the format: Title: The Go Programming Language, Author: Alan A. A. Donovan.

💡 Why This Matters

🌍 Real World

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

💼 Career

Understanding structs is essential for Go programming jobs, as they are the foundation for creating complex data models and working with APIs.

1

Define the Book struct

Define a struct named Book with two fields: Title and Author, both of type string.

Go

package main

type Book struct {
    // Your code here
}

func main() {

}

Hint

Use type Book struct {} and inside add Title string and Author string.

2

Create a myBook variable of type Book

Inside the main function, create a variable named myBook of type Book with Title set to "The Go Programming Language" and Author set to "Alan A. A. Donovan".

Go

package main

type Book struct {
    Title  string
    Author string
}

func main() {
    // Your code here
}

Hint

Use myBook := Book{Title: "The Go Programming Language", Author: "Alan A. A. Donovan"} inside main.

3

Print the book's title and author

Add a fmt.Println statement inside main to print the book's title and author in this exact format: Title: The Go Programming Language, Author: Alan A. A. Donovan. Use myBook.Title and myBook.Author.

Go

package main

import "fmt"

type Book struct {
    Title  string
    Author string
}

func main() {
    myBook := Book{
        Title:  "The Go Programming Language",
        Author: "Alan A. A. Donovan",
    }
    // Print the book details here
}

Hint

Use fmt.Println("Title:", myBook.Title+",", "Author:", myBook.Author) to print the details.

4

Run the program to see the output

Run the program to display the book's title and author exactly as: Title: The Go Programming Language, Author: Alan A. A. Donovan.

Go

package main

import "fmt"

type Book struct {
    Title  string
    Author string
}

func main() {
    myBook := Book{
        Title:  "The Go Programming Language",
        Author: "Alan A. A. Donovan",
    }
    fmt.Println("Title:", myBook.Title+",", "Author:", myBook.Author)
    // Run the program to see the output
}

Hint

Make sure the output matches exactly with the title and author separated by a comma.

Practice

1. What is the purpose of defining a struct in Go?

easy

A. To create a new function

B. To group related data fields into a single unit

C. To declare a package

D. To import external libraries

Solution

1. Step 1: Understand the role of structs

   Structs are used to group related data fields together in one unit, like a blueprint for an object.

2. Step 2: Compare with other options

   Functions, packages, and imports serve different purposes unrelated to grouping data.

3. Final Answer:

   To group related data fields into a single unit -> Option B

4. Quick Check:

   Struct = grouped data [OK]

Hint: Structs bundle related info like a real-world object [OK]

Common Mistakes:

• Confusing structs with functions
• Thinking structs declare packages
• Mixing structs with imports

2. Which of the following is the correct way to define a struct named Person with fields Name (string) and Age (int)?

easy

A. type Person { Name string; Age int }

B. struct Person { Name string; Age int }

C. type Person struct { Name string; Age int }

D. Person struct { Name string; Age int }

Solution

1. Step 1: Recall Go struct syntax

   In Go, structs are defined using the syntax: type Name struct { fields }.

2. Step 2: Check each option

   type Person struct { Name string; Age int } matches the correct syntax. Options A, B, and C miss the 'type' keyword or 'struct' keyword placement.

3. Final Answer:

   type Person struct { Name string; Age int } -> Option C

4. Quick Check:

   Correct struct syntax = type Person struct { Name string; Age int } [OK]

Hint: Remember: 'type Name struct { fields }' [OK]

Common Mistakes:

• Omitting 'type' keyword
• Missing 'struct' keyword
• Incorrect order of keywords

3. What will be the output of the following Go code?

package main
import "fmt"
type Car struct {
  Brand string
  Year  int
}
func main() {
  c := Car{Brand: "Toyota", Year: 2020}
  fmt.Println(c.Brand)
}

medium

A. Car{Brand: "Toyota", Year: 2020}

B. 2020

C. Compilation error

D. Toyota

Solution

1. Step 1: Understand struct initialization

   The struct Car is initialized with Brand="Toyota" and Year=2020.

2. Step 2: Identify printed field

   The code prints c.Brand, which is "Toyota".

3. Final Answer:

   Toyota -> Option D

4. Quick Check:

   Print c.Brand = Toyota [OK]

Hint: Print field with dot: variable.FieldName [OK]

Common Mistakes:

• Printing the whole struct instead of a field
• Confusing field names
• Expecting Year instead of Brand

4. Identify the error in the following Go code snippet:

package main
import "fmt"
type Book struct {
  Title string
  Pages int
}

func main() {
  b := Book{Title: "Go Guide", Pages: "300"}
  fmt.Println(b)
}

medium

A. Pages field has wrong type, should be int not string

B. Missing import for fmt package

C. Struct fields must be lowercase

D. Cannot print struct directly

Solution

1. Step 1: Check field types in struct initialization

   The Pages field is declared as int but assigned a string "300" which is a type mismatch.

2. Step 2: Verify other possible errors

   Import for fmt package is present. Struct fields can be uppercase. Printing structs directly is allowed.

3. Final Answer:

   Pages field has wrong type, should be int not string -> Option A

4. Quick Check:

   Type mismatch in struct field assignment [OK]

Hint: Match field types exactly when initializing structs [OK]

Common Mistakes:

• Assigning string to int field
• Expecting compilation error from printing struct
• Thinking struct fields must be lowercase

5. Given the struct definition:

type Employee struct {
  Name   string
  Salary int
  Active bool
}

Which of the following code snippets correctly creates a slice of Employee structs with only active employees having salary above 50000?

hard

A. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}}
var filtered []Employee
for _, e := range emps {
if e.Active && e.Salary > 50000 {
filtered = append(filtered, e)
}
}

B. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}}
filtered := []Employee{}
for i := range emps {
if emps[i].Salary > 50000 {
filtered = append(filtered, emps[i])
}
}

C. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}}
filtered := []Employee{}
for _, e := range emps {
if e.Active || e.Salary > 50000 {
filtered = append(filtered, e)
}
}

D. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}}
filtered := []Employee{}
for _, e := range emps {
if e.Active && e.Salary < 50000 {
filtered = append(filtered, e)
}
}

Solution

1. Step 1: Understand filtering criteria

   We want only employees who are active and have salary above 50000.

2. Step 2: Check each code snippet logic

   emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}} var filtered []Employee for _, e := range emps { if e.Active && e.Salary > 50000 { filtered = append(filtered, e) } } uses 'e.Active && e.Salary > 50000' which matches criteria. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}} filtered := []Employee{} for i := range emps { if emps[i].Salary > 50000 { filtered = append(filtered, emps[i]) } } misses active check. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}} filtered := []Employee{} for _, e := range emps { if e.Active || e.Salary > 50000 { filtered = append(filtered, e) } } uses '||' which includes inactive employees. emps := []Employee{{"Alice", 60000, true}, {"Bob", 45000, true}, {"Carol", 70000, false}} filtered := []Employee{} for _, e := range emps { if e.Active && e.Salary < 50000 { filtered = append(filtered, e) } } uses salary < 50000 which is wrong.

3. Final Answer:

   The code that filters using e.Active && e.Salary > 50000 -> Option A

4. Quick Check:

   Filter with '&&' for both conditions [OK]

Hint: Use && to combine multiple conditions correctly [OK]

Common Mistakes:

• Using || instead of && for filtering
• Ignoring the Active field in filter
• Using wrong salary comparison operator