Array declaration in Go - Mini Project: Build & Apply

Array declaration

📖 Scenario: You are organizing a small event and want to keep track of the number of guests arriving each day over a week.

🎯 Goal: Create an array to store the number of guests for each day of the week.

📋 What You'll Learn

Create an array with exactly 7 integers representing guests per day

Use the array to store the exact values given

Print the array to show the guest counts

💡 Why This Matters

🌍 Real World

Arrays are useful to store fixed sets of related data, like daily counts or measurements.

💼 Career

Understanding arrays and loops is fundamental for programming tasks in any software development job.

1

Create an array with guest counts

Create an array called guests of type [7]int with these exact values: 12, 15, 10, 20, 18, 25, 30.

Go

# Create the array 'guests' with 7 integers for each day
# Your code here

Hint

Use the syntax varName := [size]type{values} to declare and initialize an array.

2

Add a variable for total guests

Create an integer variable called totalGuests and set it to 0.

Go

package main

import "fmt"

func main() {
    guests := [7]int{12, 15, 10, 20, 18, 25, 30}
    // Create 'totalGuests' and set to 0
    // Your code here
}

Hint

Use variableName := value to create and set a variable.

3

Calculate total guests using a loop

Use a for loop with the variable i from 0 to 6 to add each day's guests from guests[i] to totalGuests.

Go

package main

import "fmt"

func main() {
    guests := [7]int{12, 15, 10, 20, 18, 25, 30}
    totalGuests := 0
    // Add guests from each day to totalGuests using a for loop
    // Your code here
}

Hint

Use a for loop with index i to access array elements by guests[i].

4

Print the total number of guests

Write a fmt.Println statement to print the text Total guests: followed by the value of totalGuests.

Go

package main

import "fmt"

func main() {
    guests := [7]int{12, 15, 10, 20, 18, 25, 30}
    totalGuests := 0
    for i := 0; i < 7; i++ {
        totalGuests += guests[i]
    }
    // Print the total guests
    // Your code here
}

Hint

Use fmt.Println("Total guests:", totalGuests) to print the message and number.

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