Array declaration in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of 5 integers.

Go

[1] numbers [5]int

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

Avar

B=

C:=

Dconst

Attempts:

3 left

💡 Hint

Common Mistakes

Using := to declare an array type

Using = sign between variable name and type

Using const keyword for array declaration

In Go, to declare an array variable, you use var followed by the variable name, then the type. The equal sign = is not used here; instead, you just write the type after the variable name. So the correct syntax is var numbers [5]int.

2fill in blank

medium

Complete the code to declare and initialize an array of 3 strings.

Go

var fruits = [1]string{"apple", "banana", "cherry"}

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

A[]

B[3]

Cmake

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using []string instead of [3]string for array

Using make function for array initialization

Using {} without type declaration

To declare and initialize an array of 3 strings, you specify the size in square brackets before the type, like [3]string. This tells Go the array has exactly 3 elements.

3fill in blank

hard

Fix the error in the array declaration to create an array of 4 floats.

Go

var values = [1]float64{1.1, 2.2, 3.3, 4.4}

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

A[]

B(4)

C[4]

D{4}

Attempts:

3 left

💡 Hint

Common Mistakes

Using []float64 which declares a slice, not an array

Using parentheses or braces for size

Omitting the size

Arrays in Go require the size inside square brackets before the type. So [4]float64 declares an array of 4 floats. Using []float64 would declare a slice, which is different.

4fill in blank

hard

Fill the blank to declare an array of 2 booleans and initialize it with true and false.

Go

var flags [1]bool = {true, false}

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

A[2]

B[3]

C[]

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using []bool which declares a slice

Using parentheses instead of curly braces for initialization

Mismatching array size and number of elements

The array size must be specified as [2] before the type. The initialization uses curly braces {} with the values inside. So the correct declaration is var flags [2]bool = {true, false}.

5fill in blank

hard

Fill both blanks to declare and initialize an array of 3 integers with values 10, 20, and 30.

Go

var nums [1]int = [2]

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

A[3]

B[4]

C{10, 20, 30}

D{10, 20, 30, 40}

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong array size

Including more elements than the size

Using slice syntax instead of array

The array size must be [3] before the type. The initialization uses curly braces with the values inside. The correct initialization is {10, 20, 30}. The extra option {10, 20, 30, 40} is a distractor and should not be used.

Practice

1. What does the following Go code declare?
var arr [3]int

easy

A. A slice of integers with length 3

B. An array of 3 integers initialized with zero values

C. A pointer to an integer array

D. A map with integer keys and values

Solution

1. Step 1: Understand the syntax var arr [3]int

   This declares a fixed-size array named arr with 3 elements, each of type int.

2. Step 2: Recognize default initialization

   In Go, arrays are initialized with zero values for their type, so all 3 integers start as 0.

3. Final Answer:

   An array of 3 integers initialized with zero values -> Option B

4. Quick Check:

   Array declaration = fixed size + type + zero values [OK]

Hint: Remember: [n]type means fixed size array of n elements [OK]

Common Mistakes:

• Confusing array with slice declaration
• Thinking it creates a pointer or map
• Assuming uninitialized values are random

2. Which of the following is the correct way to declare an array of 4 strings in Go?

easy

A. var arr [4]string

B. var arr []string{4}

C. arr := [4]string{}

D. var arr string[4]

Solution

1. Step 1: Check Go array declaration syntax

   Arrays are declared with var name [size]type. So var arr [4]string is correct.

2. Step 2: Analyze other options

   var arr []string{4} uses slice syntax incorrectly. arr := [4]string{} is valid short declaration syntax in Go. var arr string[4] reverses size and type, which is invalid.

3. Final Answer:

   var arr [4]string -> Option A

4. Quick Check:

   Array syntax = var name [size]type [OK]

Hint: Array size goes inside brackets before type [OK]

Common Mistakes:

• Using slice syntax instead of array syntax
• Placing size after type
• Missing var keyword or wrong initialization

3. What is the output of this Go program?

package main
import "fmt"
func main() {
  var nums = [3]int{10, 20, 30}
  fmt.Println(nums[1])
}

medium

A. 10

B. 0

C. 30

D. 20

Solution

1. Step 1: Understand array initialization

   The array nums has 3 integers: 10 at index 0, 20 at index 1, and 30 at index 2.

2. Step 2: Access element at index 1

   Printing nums[1] outputs the second element, which is 20.

3. Final Answer:

   20 -> Option D

4. Quick Check:

   Array index starts at 0, nums[1] = 20 [OK]

Hint: Array indexes start at 0; second element is index 1 [OK]

Common Mistakes:

• Confusing index 1 with index 0
• Expecting output 10 or 30 instead of 20
• Thinking array is zero-indexed but printing wrong element

4. Identify the error in this Go array declaration:

var arr [3]int = {1, 2, 3}

medium

A. Array initialization syntax is incorrect

B. Braces {} should be replaced with []

C. Missing keyword 'var'

D. Array size must be omitted

Solution

1. Step 1: Review array initialization syntax

   In Go, when initializing an array with values, the correct syntax is var arr = [3]int{1, 2, 3} or arr := [3]int{1, 2, 3}.

2. Step 2: Identify the error

   The code uses var arr [3]int = {1, 2, 3} which misses the array type on the right side before the braces. This causes a syntax error.

3. Final Answer:

   Array initialization syntax is incorrect -> Option A

4. Quick Check:

   Array init needs type before braces [OK]

Hint: Array init needs type before braces, like [3]int{...} [OK]

Common Mistakes:

• Omitting array type on right side during initialization
• Using wrong braces or brackets
• Trying to assign without proper syntax

5. How can you declare and initialize a 2D array of integers with 2 rows and 3 columns in Go?

hard

A. var matrix [2][3]int = [2][3]int{{1,2,3},{4,5,6}}

B. var matrix [][]int = {{1,2,3},{4,5,6}}

C. matrix := [2][3]int{{1,2,3},{4,5,6}}

D. var matrix [3][2]int = {{1,2},{3,4},{5,6}}

Solution

1. Step 1: Understand 2D array declaration

   A 2D array with 2 rows and 3 columns is declared as [2][3]int. Both dimensions must be specified.

2. Step 2: Check initialization syntax

   matrix := [2][3]int{{1,2,3},{4,5,6}} uses short declaration with := and correctly initializes the 2D array with two rows of three integers each.

3. Step 3: Analyze other options

   var matrix [2][3]int = [2][3]int{{1,2,3},{4,5,6}} is correct syntax but uses explicit var with type on both sides (valid but less common). var matrix [][]int = {{1,2,3},{4,5,6}} is a slice of slices, not an array. var matrix [3][2]int = {{1,2},{3,4},{5,6}} has dimensions reversed (3 rows, 2 columns).

4. Final Answer:

   matrix := [2][3]int{{1,2,3},{4,5,6}} -> Option C

5. Quick Check:

   2D array = [rows][cols]type with nested braces [OK]

Hint: Use [rows][cols]type with nested braces to initialize [OK]

Common Mistakes:

• Confusing slices with arrays
• Swapping row and column sizes
• Missing nested braces for 2D arrays