Why pointers are needed in Go - See It in Action

Why pointers are needed

📖 Scenario: Imagine you have a list of boxes, each with a number inside. You want to change the number inside a box without making a copy of the box. This is like using pointers in Go.

🎯 Goal: You will create a simple Go program that shows how pointers let you change the original value of a variable by using its address.

📋 What You'll Learn

Create an integer variable called number with the value 10

Create a pointer variable called ptr that points to number

Change the value of number through the pointer ptr to 20

Print the value of number to show it has changed

💡 Why This Matters

🌍 Real World

Pointers are used in real programs to efficiently update data without copying it, like changing settings or updating large data structures.

💼 Career

Understanding pointers is important for Go developers to write efficient and clear code, especially when working with functions, data structures, and system programming.

1

Create an integer variable

Create an integer variable called number and set it to 10.

Go

package main

func main() {
    // Create an integer variable called number and set it to 10
    // Your code here
}

Hint

Use := to create and set the variable in one line.

2

Create a pointer to the variable

Create a pointer variable called ptr that stores the address of number using the & operator.

Go

package main

func main() {
    number := 10
    // Create a pointer variable ptr that points to number
    // Your code here
}

Hint

Use &number to get the address of the variable number.

3

Change the value using the pointer

Use the pointer ptr to change the value of number to 20. Use the * operator to access the value at the pointer.

Go

package main

func main() {
    number := 10
    ptr := &number
    // Change the value of number to 20 using ptr
    // Your code here
}

Hint

Use *ptr = 20 to set the value at the address stored in ptr.

4

Print the changed value

Print the value of number using fmt.Println(number) to show it has changed to 20. Remember to import fmt.

Go

package main

import "fmt"

func main() {
    number := 10
    ptr := &number
    *ptr = 20
    // Print the value of number
    // Your code here
}

Hint

Use fmt.Println(number) to print the value.

Practice

1. Why do we need pointers in Go programming?

easy

A. To make the program run slower

B. To allow functions to modify the original variable's value

C. To create new variables automatically

D. To avoid using variables altogether

Solution

1. Step 1: Understand what pointers do

   Pointers hold the memory address of a variable, not a copy of its value.

2. Step 2: Why modify original data matters

   Using pointers lets functions change the actual variable, not just a copy, which is efficient and necessary in many cases.

3. Final Answer:

   To allow functions to modify the original variable's value -> Option B

4. Quick Check:

   Pointers let functions change original data = C [OK]

Hint: Pointers let functions change original data, not copies [OK]

Common Mistakes:

• Thinking pointers create new variables
• Believing pointers slow down programs
• Assuming pointers avoid variables

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

easy

A. var p *int

B. var p int*

C. var *p int

D. var p &int

Solution

1. Step 1: Recall Go pointer syntax

   In Go, a pointer type is written as * followed by the type, e.g., *int for pointer to int.

2. Step 2: Match syntax to options

   var p *int uses 'var p *int', which is the correct syntax for declaring a pointer to int.

3. Final Answer:

   var p *int -> Option A

4. Quick Check:

   Pointer declaration = var p *int [OK]

Hint: Pointer type uses * before type, like *int [OK]

Common Mistakes:

• Placing * after variable name
• Using & instead of * for pointer type
• Mixing pointer syntax with other languages

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

package main
import "fmt"
func main() {
    x := 10
    changeValue(&x)
    fmt.Println(x)
}

func changeValue(p *int) {
    *p = 20
}

medium

A. 20

B. Compilation error

C. 0

D. 10

Solution

1. Step 1: Understand pointer usage in changeValue

   The function receives a pointer to x, so *p = 20 changes the original x value to 20.

2. Step 2: Print the updated value of x

   After calling changeValue, x is updated to 20, so fmt.Println(x) prints 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   Pointer changes original variable = 20 [OK]

Hint: Pointer lets function change original variable value [OK]

Common Mistakes:

• Thinking x remains 10 because of pass by value
• Confusing pointer dereference syntax
• Expecting compilation error due to pointer

4. Identify the error in this Go code that tries to update a variable using a pointer:

package main
import "fmt"
func main() {
    x := 5
    changeValue(x)
    fmt.Println(x)
}

func changeValue(p *int) {
    *p = 10
}

medium

A. No error, code works fine

B. changeValue should not use pointers

C. x should be a pointer variable

D. Missing & when calling changeValue

Solution

1. Step 1: Check how changeValue is called

   changeValue expects a pointer (*int), but main passes x (int) without & operator.

2. Step 2: Correct call with pointer

   To fix, call changeValue(&x) to pass the address of x.

3. Final Answer:

   Missing & when calling changeValue -> Option D

4. Quick Check:

   Pass pointer with & operator = A [OK]

Hint: Pass variable address with & when function expects pointer [OK]

Common Mistakes:

• Passing variable instead of its address
• Changing function signature unnecessarily
• Assuming no error occurs

5. You want to write a function in Go that swaps the values of two integers. Why must you use pointers for the parameters?

hard

A. Because Go does not allow returning multiple values

B. Because pointers make the function run slower

C. Because passing by value copies variables, so original values won't change

D. Because pointers automatically create new variables

Solution

1. Step 1: Understand parameter passing in Go

   Go passes arguments by value, so without pointers, the function works on copies.

2. Step 2: Why pointers are needed for swapping

   Using pointers lets the function access and modify the original variables, enabling the swap.

3. Final Answer:

   Because passing by value copies variables, so original values won't change -> Option C

4. Quick Check:

   Pointers needed to modify originals, not copies = B [OK]

Hint: Swap needs pointers to change original variables [OK]

Common Mistakes:

• Thinking Go can't return multiple values
• Believing pointers slow down swap
• Assuming pointers create new variables