Struct pointers in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a pointer to a struct variable.

Go

var p [1] Person

Drag options to blanks, or click blank then click option'

A%

B&

C->

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using & instead of * to declare a pointer type.

Using -> which is not valid in Go.

In Go, a pointer to a struct is declared using the * symbol before the struct type.

2fill in blank

medium

Complete the code to assign the address of a struct variable to a pointer.

Go

p = [1]person

Drag options to blanks, or click blank then click option'

A&

B*

C->

D%

Attempts:

3 left

💡 Hint

Common Mistakes

Using * instead of & to get the address.

Using -> which is invalid in Go.

Use the & operator to get the address of a variable in Go.

3fill in blank

hard

Fix the error in accessing a struct field through a pointer.

Go

fmt.Println(p[1]Name)

Drag options to blanks, or click blank then click option'

A.

B->

C*.

D&.

Attempts:

3 left

💡 Hint

Common Mistakes

Using -> which is invalid in Go.

Trying to dereference manually with *.

In Go, you access struct fields through a pointer using the dot . operator directly; Go automatically dereferences the pointer.

4fill in blank

hard

Fill both blanks to create a pointer to a struct and assign it.

Go

p := [1]Person[2]

Drag options to blanks, or click blank then click option'

A&

B*

C{}

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using * instead of & to get the address.

Using [] which is for slices, not structs.

Use & to get the address of a struct literal Person{}.

5fill in blank

hard

Fill all three blanks to create a map with struct pointers and filter by a field.

Go

result := map[string]*Person{ [1]: [2]Person{Name: "Alice"} }
filtered := map[string]*Person{}
for k, v := range result {
  if v.Name [3] "Alice" {
    filtered[k] = v
  }
}

Drag options to blanks, or click blank then click option'

A"user1"

B&

C==

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using : instead of : in map literal key-value pair.

Not using & to get pointer to struct.

Using = instead of == for comparison.

Use a key string "user1", get the address of the struct with &, and compare the field with ==.

Practice

1. What does a struct pointer in Go hold?
type Person struct { Name string }

easy

A. Only the struct's first field value

B. A copy of the struct data

C. The memory address of a struct instance

D. A string representation of the struct

Solution

1. Step 1: Understand what a pointer stores

   A pointer stores the memory address of a variable, not the variable's value itself.

2. Step 2: Apply to struct pointers

   A struct pointer holds the address of the struct instance, allowing access or modification of the original struct.

3. Final Answer:

   The memory address of a struct instance -> Option C

4. Quick Check:

   Struct pointer = memory address [OK]

Hint: Pointers hold addresses, not copies. Remember & for address [OK]

Common Mistakes:

• Thinking pointer holds a copy of the struct
• Confusing pointer with struct value
• Assuming pointer holds only first field

2. Which of the following is the correct way to declare a pointer to a struct Person in Go?

easy

A. var *p Person

B. var p Person*

C. var p &Person

D. var p *Person

Solution

1. Step 1: Recall Go pointer syntax

   In Go, a pointer type is declared by placing * before the type name, e.g., *Person.

2. Step 2: Match correct declaration

   var p *Person uses var p *Person, which is the correct syntax for a pointer variable.

3. Final Answer:

   var p *Person -> Option D

4. Quick Check:

   Pointer declaration = *Type [OK]

Hint: Pointer type syntax: *TypeName, not after variable [OK]

Common Mistakes:

• Placing * after variable name
• Using & in declaration instead of *
• Incorrect order of * and type

3. What is the output of this Go program?

package main
import "fmt"
type Point struct { X, Y int }
func main() {
 p := Point{1, 2}
 ptr := &p
 ptr.X = 10
 fmt.Println(p.X)
}

medium

A. 1

B. 10

C. 0

D. Compilation error

Solution

1. Step 1: Understand pointer modification

   ptr points to p. Changing ptr.X modifies p.X because ptr references p's memory.

2. Step 2: Check printed value

   After setting ptr.X = 10, p.X becomes 10. So, printing p.X outputs 10.

3. Final Answer:

   10 -> Option B

4. Quick Check:

   Pointer changes original struct field [OK]

Hint: Changing pointer field changes original struct field [OK]

Common Mistakes:

• Thinking ptr.X is separate copy
• Expecting original p.X to remain 1
• Confusing pointer dereference syntax

4. Identify the error in this Go code snippet:

package main
import "fmt"
type User struct { Name string }
func updateName(u User) {
 u.Name = "Alice"
}
func main() {
 user := User{"Bob"}
 updateName(&user)
 fmt.Println(user.Name)
}

medium

A. Passing pointer to function expecting value

B. Missing import for fmt package

C. Cannot assign string to Name field

D. Function parameter should be a pointer to User

Solution

1. Step 1: Check function parameter type

   Function updateName expects a User value, but main passes &user (a *User pointer).

2. Step 2: Identify the type mismatch

   This causes a compilation error because the argument type (*User) does not match the parameter type (User).

3. Final Answer:

   Passing pointer to function expecting value -> Option A

4. Quick Check:

   Function param must match argument type [OK]

Hint: Match function param type with argument (& for pointer) [OK]

Common Mistakes:

• Passing pointer to value parameter without pointer receiver
• Ignoring need to modify original struct
• Assuming string assignment causes error

5. Given this struct and function:

package main
import "fmt"
type Counter struct { Count int }
func increment(c *Counter) {
 c.Count++
}
func main() {
 c := Counter{Count: 5}
 increment(&c)
 increment(c)
 fmt.Println(c.Count)
}

What will happen when running this program?

hard

A. Compilation error at increment(c)

B. Output is 7

C. Output is 6

D. Runtime panic due to invalid pointer

Solution

1. Step 1: Analyze function calls

   increment expects a *Counter pointer. The first call increment(&c) is correct.

2. Step 2: Check second call increment(c)

   Passing c (a value) instead of *Counter causes a compilation error because types don't match.

3. Final Answer:

   Compilation error at increment(c) -> Option A

4. Quick Check:

   Pointer param requires pointer argument [OK]

Hint: Pointer params need pointer args; value won't auto-convert [OK]

Common Mistakes:

• Assuming Go auto-converts value to pointer
• Expecting output 7 without error
• Ignoring type mismatch in function call