Struct pointers in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of struct pointer field modification

What is the output of this Go program?

Go

package main
import "fmt"
type Person struct {
    Name string
    Age  int
}
func main() {
    p := Person{"Alice", 30}
    ptr := &p
    ptr.Age = 31
    fmt.Println(p.Age)
}

A Compilation error

B 0

C 30

D 31

💡 Hint

Remember that modifying a struct through its pointer changes the original struct.

The pointer ptr points to p. Changing ptr.Age changes p.Age because ptr references p directly.

❓ Predict Output

intermediate

Output when assigning struct pointer to another variable

What will be printed by this Go program?

Go

package main
import "fmt"
type Point struct {
    X, Y int
}
func main() {
    p1 := &Point{X: 1, Y: 2}
    p2 := p1
    p2.X = 10
    fmt.Println(p1.X)
}

A 0

B 1

C 10

D Compilation error

💡 Hint

Both p1 and p2 point to the same struct in memory.

p2 is assigned the pointer p1, so both point to the same Point struct. Changing p2.X changes p1.X.

🔧 Debug

advanced

Identify the runtime error in struct pointer usage

What error does this Go program produce when run?

Go

package main
import "fmt"
type Data struct {
    Value int
}
func main() {
    var d *Data
    d.Value = 5
    fmt.Println(d.Value)
}

A panic: runtime error: invalid memory address or nil pointer dereference

B Output: 5

C Compilation error: cannot assign to d.Value

D No output, program hangs

💡 Hint

Check if the pointer d is initialized before accessing its fields.

d is a nil pointer. Accessing d.Value causes a runtime panic due to nil pointer dereference.

🧠 Conceptual

advanced

Effect of passing struct pointer to a function

Consider this Go code snippet. What will be the output after calling updateAge(&p)?

Go

package main
import "fmt"
type Person struct {
    Age int
}
func updateAge(p *Person) {
    p.Age = 40
}
func main() {
    p := Person{Age: 25}
    updateAge(&p)
    fmt.Println(p.Age)
}

A 25

B 40

C 0

D Compilation error

💡 Hint

Passing a pointer allows the function to modify the original struct.

The function receives a pointer to p and sets p.Age to 40, modifying the original struct.

🔧 Debug

expert

Which option causes a runtime panic with struct pointers?

Given the struct type Node, which code snippet will cause a runtime panic?

Go

type Node struct {
    Value int
    Next  *Node
}

A

var n *Node
n.Value = 10

B

n := &Node{Value: 5}
n.Next = &Node{Value: 10}

C

var n Node
n.Value = 3

D

n := Node{Value: 1}
var p *Node = &n
p.Value = 2

💡 Hint

Check if the pointer variable is initialized before accessing fields.

Option A declares a nil pointer n and accesses n.Value, causing a runtime panic due to nil pointer dereference.