Pointer behavior in functions in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Go code with pointer parameter?

Consider this Go program that modifies a variable through a pointer parameter. What will it print?

Go

package main
import "fmt"

func modify(x *int) {
    *x = *x + 10
}

func main() {
    a := 5
    modify(&a)
    fmt.Println(a)
}

A 5

B 10

C 15

D Compilation error

💡 Hint

Think about what happens when you change the value at the memory address the pointer points to.

The function modify receives a pointer to a. It adds 10 to the value at that address. So a becomes 15.

❓ Predict Output

intermediate

What does this Go code print when passing a pointer to a struct?

Look at this Go code that changes a struct field via a pointer. What is printed?

Go

package main
import "fmt"

type Point struct {
    x int
    y int
}

func move(p *Point) {
    p.x = 10
    p.y = 20
}

func main() {
    pt := Point{1, 2}
    move(&pt)
    fmt.Println(pt.x, pt.y)
}

A 1 2

B 10 20

C 0 0

D Compilation error

💡 Hint

Remember that pointers to structs allow modifying the original struct fields.

The move function changes the fields of the struct via the pointer. So the original struct's fields become 10 and 20.

🔧 Debug

advanced

Why does this Go function not change the original variable?

Examine this Go code. The function tries to change the value of num but it does not work. Why?

Go

package main
import "fmt"

func changeValue(x int) {
    x = 100
}

func main() {
    num := 50
    changeValue(num)
    fmt.Println(num)
}

A Because <code>changeValue</code> receives a copy of <code>num</code>, not a pointer

B Because <code>num</code> is a constant and cannot be changed

C Because the function has a syntax error and does not run

D Because <code>num</code> is declared inside <code>main</code> and is not accessible

💡 Hint

Think about how Go passes arguments to functions by default.

In Go, function parameters are passed by value. So changeValue gets a copy of num. Changing x inside the function does not affect num.

📝 Syntax

advanced

Which option correctly declares a function that takes a pointer to int in Go?

Choose the correct Go function signature that accepts a pointer to an int.

A func update(x *int) {}

B func update(*int x) {}

C func update(int *x) {}

D func update(x int*) {}

💡 Hint

In Go, the pointer symbol * goes before the type, not the variable name.

The correct syntax is func update(x *int). The pointer symbol * is before the type int. Other options are invalid syntax.

🚀 Application

expert

How many items are in the slice after this function modifies it via pointer?

Consider this Go code that appends to a slice via a pointer. How many elements does the slice have after calling appendValue?

Go

package main
import "fmt"

func appendValue(s *[]int, v int) {
    *s = append(*s, v)
}

func main() {
    nums := []int{1, 2, 3}
    appendValue(&nums, 4)
    fmt.Println(len(nums))
}

A 3

B Compilation error

C 0

D 4

💡 Hint

Appending to a slice inside a function requires updating the original slice via pointer.

The function appends 4 to the slice by dereferencing the pointer and assigning the new slice back. So the slice length becomes 4.