Nested structs in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested struct field access

What is the output of this Go program?

Go

package main
import "fmt"
type Address struct {
    City string
    Zip  int
}
type Person struct {
    Name    string
    Address Address
}
func main() {
    p := Person{Name: "Alice", Address: Address{City: "Paris", Zip: 75000}}
    fmt.Println(p.Address.City)
}

A 75000

B Address{City: "Paris", Zip: 75000}

C Alice

D Paris

💡 Hint

Look at how nested structs are accessed using dot notation.

The field City is inside the nested Address struct. Accessing p.Address.City prints "Paris".

❓ Predict Output

intermediate

Output of nested struct pointer access

What will this Go program print?

Go

package main
import "fmt"
type Engine struct {
    Horsepower int
}
type Car struct {
    Model  string
    Engine *Engine
}
func main() {
    e := Engine{Horsepower: 300}
    c := Car{Model: "Mustang", Engine: &e}
    fmt.Println(c.Engine.Horsepower)
}

A Mustang

B nil

C 300

D 0

💡 Hint

Remember to dereference pointers automatically with dot notation.

The Engine field is a pointer to Engine struct. Accessing c.Engine.Horsepower prints 300.

🔧 Debug

advanced

Identify the compilation error in nested struct initialization

This Go code does not compile. What is the cause of the error?

Go

package main
import "fmt"
type Point struct {
    X, Y int
}
type Rectangle struct {
    TopLeft, BottomRight Point
}
func main() {
    r := Rectangle{TopLeft: Point{X: 0, Y: 10}, BottomRight: Point{X: 5, Y: 0}}
    fmt.Println(r)
}

A Missing type name in nested struct literals

B Cannot use composite literals inside struct initialization

C Fields TopLeft and BottomRight are unexported

D fmt.Println cannot print structs

💡 Hint

Check how nested structs are initialized in Go.

In Go, nested struct literals must include the type name. Using {X:0, Y:10} alone causes a syntax error.

❓ Predict Output

advanced

Output of embedded struct field promotion

What does this Go program print?

Go

package main
import "fmt"
type Contact struct {
    Email string
}
type Employee struct {
    Name    string
    Contact
}
func main() {
    e := Employee{Name: "Bob", Contact: Contact{Email: "[e-mail]"}}
    fmt.Println(e.Email)
}

A Name field value: Bob

B [e-mail]

C Compilation error: ambiguous field

D Contact{Email: "[e-mail]"}

💡 Hint

Embedded structs promote their fields to the outer struct.

The embedded Contact struct's Email field is promoted, so e.Email accesses it directly.

🧠 Conceptual

expert

Number of fields in nested and embedded structs

Given these struct definitions, how many fields does variable 'd' of type Developer have?

Go

type Address struct {
    City string
    Zip  int
}
type Contact struct {
    Email string
    Phone string
}
type Developer struct {
    Name    string
    Address
    Contact
}

A 5

B 3

C 4

D 6

💡 Hint

Count all fields including embedded struct fields promoted to Developer.

Developer has Name plus all fields from Address (City, Zip) and Contact (Email, Phone), total 5 fields.

Practice

1. What is the main purpose of using nested structs in Go?

easy

A. To group related data together inside another struct

B. To create multiple independent structs

C. To make the program run faster

D. To avoid using functions

Solution

1. Step 1: Understand struct grouping

   Nested structs allow one struct to contain another, grouping related data logically.

2. Step 2: Compare options

   Creating multiple independent structs, making the program run faster, or avoiding functions do not describe grouping data inside structs.

3. Final Answer:

   To group related data together inside another struct -> Option A

4. Quick Check:

   Nested structs = Group related data [OK]

Hint: Think of nested structs as folders inside folders [OK]

Common Mistakes:

• Confusing nested structs with separate structs
• Thinking nested structs improve speed
• Believing nested structs replace functions

2. Which of the following is the correct way to access the field City inside a nested struct Address within struct Person?

easy

A. person.City.Address

B. person->Address->City

C. person.Address.City

D. person.Address->City

Solution

1. Step 1: Recall Go syntax for nested structs

   Access nested fields using dot notation: Outer.Inner.Field.

2. Step 2: Evaluate options

   person.Address.City uses correct dot notation. Arrow syntax (->) is invalid in Go. person.City.Address reverses the order.

3. Final Answer:

   person.Address.City -> Option C

4. Quick Check:

   Dot notation = person.Address.City [OK]

Hint: Use dot notation to access nested fields [OK]

Common Mistakes:

• Using arrow (->) instead of dot (.)
• Reversing the order of fields
• Trying to access nested fields directly without parent

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

package main
import "fmt"
type Address struct {
    City string
    Zip  int
}
type Person struct {
    Name    string
    Address Address
}
func main() {
    p := Person{Name: "Anna", Address: Address{City: "Paris", Zip: 75000}}
    fmt.Println(p.Address.City)
}

medium

A. Anna

B. Paris

C. 75000

D. Address

Solution

1. Step 1: Understand struct initialization

   Person struct has Name and Address fields. Address is initialized with City "Paris" and Zip 75000.

2. Step 2: Identify printed field

   The code prints p.Address.City, which is "Paris".

3. Final Answer:

   Paris -> Option B

4. Quick Check:

   p.Address.City = Paris [OK]

Hint: Print nested field with dot notation [OK]

Common Mistakes:

• Printing the wrong field like Name or Zip
• Confusing struct field names
• Expecting the whole struct to print

4. Identify the error in this Go code snippet involving nested structs:

package main
import "fmt"
type Engine struct {
    Power int
}
type Car struct {
    Model  string
    Engine Engine
}
func main() {
    c := Car{Model: "Sedan"}
    fmt.Println(c.Engine.Power)
}

medium

A. c.Engine.Power is zero value, no error

B. Car struct missing Engine field

C. Engine struct is not defined

D. Cannot print nested struct fields directly

Solution

1. Step 1: Check struct definitions

   Engine and Car structs are defined correctly. Car has Engine field.

2. Step 2: Analyze initialization and print

   Car instance c is created with Model only. Engine field is zero-valued (Power = 0). Printing c.Engine.Power prints 0 without error.

3. Final Answer:

   c.Engine.Power is zero value, no error -> Option A

4. Quick Check:

   Uninitialized nested struct fields have zero values [OK]

Hint: Uninitialized nested structs have zero values [OK]

Common Mistakes:

• Assuming missing initialization causes error
• Thinking nested fields can't be printed
• Confusing missing fields with zero values

5. Given the structs below, how would you write a function FullAddress that returns a formatted string combining Street, City, and Zip from nested structs?

type Location struct {
    Street string
    City   string
}
type Address struct {
    Location Location
    Zip      int
}

hard

A. func FullAddress(a Address) string { return a.Street + ", " + a.City + " " + fmt.Sprint(a.Zip) }

B. func FullAddress(a Address) string { return a.Street + ", " + a.Location.City + " " + fmt.Sprint(a.Zip) }

C. func FullAddress(a Address) string { return a.Location.Street + ", " + a.City + " " + fmt.Sprint(a.Zip) }

D. func FullAddress(a Address) string { return a.Location.Street + ", " + a.Location.City + " " + fmt.Sprint(a.Zip) }

Solution

1. Step 1: Identify nested fields

   Street and City are inside Location struct, which is nested inside Address.

2. Step 2: Access nested fields correctly

   Use a.Location.Street and a.Location.City to access those fields, and a.Zip for Zip code.

3. Step 3: Check options

   Only func FullAddress(a Address) string { return a.Location.Street + ", " + a.Location.City + " " + fmt.Sprint(a.Zip) } correctly accesses nested fields with dot notation.

4. Final Answer:

   func FullAddress(a Address) string { return a.Location.Street + ", " + a.Location.City + " " + fmt.Sprint(a.Zip) } -> Option D

5. Quick Check:

   Access nested fields with dot notation [OK]

Hint: Use dot notation for each nested level [OK]

Common Mistakes:

• Accessing nested fields directly without parent struct
• Mixing field names from different structs
• Forgetting to convert int Zip to string