Array length in Go - Mini Project: Build & Apply

Array length

📖 Scenario: You are working on a program that needs to know how many items are in a list of fruits. This is common when you want to count things in real life, like how many apples you have in a basket.

🎯 Goal: Build a Go program that creates an array of fruits, then finds and prints the length of that array.

📋 What You'll Learn

Create an array called fruits with exactly these values: "apple", "banana", "cherry", "date"

Create a variable called length that stores the length of the fruits array

Print the value of length to show how many fruits are in the array

💡 Why This Matters

🌍 Real World

Counting items in a list is common in many programs, like counting products in a shopping cart or names in a guest list.

💼 Career

Knowing how to find the length of arrays or lists is a basic skill for programming jobs that involve data processing or user input.

1

Create the fruits array

Create an array called fruits with these exact string values: "apple", "banana", "cherry", "date"

Go

# Create the fruits array with the given values
# Your code here

Hint

Use square brackets with the number 4 to create an array of 4 strings.

2

Create the length variable

Create a variable called length that stores the length of the fruits array using the built-in len function

Go

package main

func main() {
    fruits := [4]string{"apple", "banana", "cherry", "date"}
    // Create length variable to store the length of fruits
    // Your code here
}

Hint

Use len(fruits) to get the number of items in the array.

3

Print the length

Use fmt.Println to print the value of the length variable

Go

package main

import "fmt"

func main() {
    fruits := [4]string{"apple", "banana", "cherry", "date"}
    length := len(fruits)
    // Print the length variable
    // Your code here
}

Hint

Use fmt.Println(length) to show the number of fruits.

4

Run the program to see the output

Run the program and observe the output. It should print the number 4 because there are four fruits in the array.

Go

package main

import "fmt"

func main() {
    fruits := [4]string{"apple", "banana", "cherry", "date"}
    length := len(fruits)
    fmt.Println(length) // This will print the length
}

Hint

The program should print 4 because there are four items in the array.

Practice

1. What does the len() function return when used with an array in Go?

easy

A. The memory size of the array in bytes

B. The number of elements in the array

C. The capacity of the array's underlying slice

D. The last element of the array

Solution

1. Step 1: Understand the purpose of len() in Go

   The len() function returns the count of elements in arrays, slices, maps, and strings.

2. Step 2: Apply len() to an array

   When used on an array, len() returns the fixed number of elements it holds.

3. Final Answer:

   The number of elements in the array -> Option B

4. Quick Check:

   len(array) = number of elements [OK]

Hint: len() always gives count of elements in an array [OK]

Common Mistakes:

• Confusing len() with capacity
• Thinking len() returns memory size
• Assuming len() returns last element

2. Which of the following is the correct way to get the length of an array named arr in Go?

easy

A. len(arr)

B. arr.length

C. size(arr)

D. length(arr)

Solution

1. Step 1: Recall Go syntax for length

   In Go, the built-in function len() is used to get the length of arrays and slices.

2. Step 2: Check each option

   Only len(arr) is valid syntax; others are invalid or do not exist in Go.

3. Final Answer:

   len(arr) -> Option A

4. Quick Check:

   Use len() function for array length [OK]

Hint: Use len(array) to get length, not dot or other functions [OK]

Common Mistakes:

• Using dot notation like arr.length
• Using non-existent functions like length() or size()
• Confusing with other languages' syntax

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

package main
import "fmt"
func main() {
    arr := [4]int{10, 20, 30, 40}
    fmt.Println(len(arr))
}

medium

A. 0

B. 3

C. 4

D. Compilation error

Solution

1. Step 1: Analyze the array declaration

   The array arr is declared with 4 elements: 10, 20, 30, 40.

2. Step 2: Understand len(arr)

   The len() function returns the number of elements, which is 4.

3. Final Answer:

   4 -> Option C

4. Quick Check:

   len([4]int{...}) = 4 [OK]

Hint: Count elements inside [ ] to find length [OK]

Common Mistakes:

• Counting elements incorrectly
• Thinking len() returns last index (3)
• Expecting runtime error

4. Identify the error in this Go code snippet:

package main
import "fmt"
func main() {
    arr := [3]int{1, 2, 3}
    fmt.Println(len(arr))
    fmt.Println(arr[3])
}

medium

A. fmt.Println cannot print arrays

B. len(arr) is invalid for arrays

C. Array declaration syntax is wrong

D. Accessing arr[3] causes an index out of range error

Solution

1. Step 1: Check array length and indexing

   The array arr has length 3, so valid indices are 0, 1, and 2.

2. Step 2: Identify invalid index access

   Accessing arr[3] is out of range and causes a runtime panic.

3. Final Answer:

   Accessing arr[3] causes an index out of range error -> Option D

4. Quick Check:

   Array indices go from 0 to len-1 [OK]

Hint: Array indices start at 0, max index = length-1 [OK]

Common Mistakes:

• Assuming len(arr) is invalid
• Thinking fmt.Println can't print arrays
• Confusing array length with capacity

5. Given two arrays in Go:

arr1 := [5]int{1, 2, 3, 4, 5}
arr2 := [3]int{10, 20, 30}

Which expression correctly checks if arr2 has fewer elements than arr1?

hard

A. len(arr2) < len(arr1)

B. len(arr1) < len(arr2)

C. arr2.length < arr1.length

D. size(arr2) < size(arr1)

Solution

1. Step 1: Identify lengths of both arrays

   arr1 has length 5, arr2 has length 3.

2. Step 2: Write correct comparison syntax

   Use len() to get lengths. To check if arr2 is smaller, compare len(arr2) < len(arr1).

3. Final Answer:

   len(arr2) < len(arr1) -> Option A

4. Quick Check:

   len(arr2) = 3 < 5 = len(arr1) [OK]

Hint: Use len() and compare lengths directly [OK]

Common Mistakes:

• Using wrong function names like length or size
• Reversing comparison order
• Using dot notation for length