Common slice operations in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a slice of integers with length 3.

Go

numbers := make([]int, [1])

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

A5

B0

C3

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using the capacity instead of length.

Confusing length with the initial values.

The make function creates a slice with the specified length. Here, length 3 means the slice has 3 elements.

2fill in blank

medium

Complete the code to append the value 7 to the slice named nums.

Go

nums = append(nums, [1])

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

A0

B7

C5

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Appending a wrong number.

Forgetting to assign the result back to the slice.

The append function adds the given value to the end of the slice. Here, we add 7.

3fill in blank

hard

Fix the error in the code to get the first element of the slice data.

Go

first := data[1]

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

A<0>

B(0)

C{0}

D[0]

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or braces instead of square brackets.

Using an index out of range.

In Go, to access an element of a slice, use square brackets with the index inside, like data[0].

4fill in blank

hard

Fill both blanks to create a new slice sub that contains elements from index 1 to 3 (exclusive) of items.

Go

sub := items[[1]:[2]]

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

A1

B2

C4

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong end index that includes unwanted elements.

Confusing inclusive and exclusive indexes.

Slicing in Go uses the syntax slice[start:end]. The slice includes elements from start up to but not including end. To get elements at indexes 1 and 2, use 1 and 3.

5fill in blank

hard

Fill all three blanks to create a map named lengths where keys are words in words slice and values are their lengths, but only for words longer than 3 characters.

Go

lengths := map[string]int{}

for _, word := range words {
    if len(word) [3] 3 {
        lengths[[1]] = [2]
    }
}

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

Aword

Blen(word)

C>

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Mixing up keys and values in the map.

The map keys are words, so word is the key. The values are lengths, so len(word) is the value. The condition checks if the word length is greater than 3, so use >.

Practice

1. What does the slice expression mySlice[2:5] do in Go?

easy

A. It returns a new slice containing elements from index 2 up to, but not including, index 5.

B. It returns elements from index 2 to index 5, including index 5.

C. It removes elements from index 2 to 5 from the original slice.

D. It appends elements from index 2 to 5 to the original slice.

Solution

1. Step 1: Understand slice syntax

   The slice expression mySlice[2:5] extracts elements starting at index 2 up to, but not including, index 5. Go slices use half-open intervals, so the element at index 5 is not included in the new slice.

2. Final Answer:

   It returns a new slice containing elements from index 2 up to, but not including, index 5. -> Option A

3. Quick Check:

   Slice[start:end] excludes end index [OK]

Hint: Remember slice end index is excluded in Go slices [OK]

Common Mistakes:

• Including the end index element in the slice
• Thinking slice removes elements from original
• Confusing append with slicing

2. Which of the following is the correct way to append an element 5 to a slice nums in Go?

easy

A. append(nums, 5)

B. nums += 5

C. nums.append(5)

D. nums = append(nums, 5)

Solution

1. Step 1: Recall append function usage

   In Go, append returns a new slice with the element added, so you must assign it back. nums = append(nums, 5) correctly assigns the result back to nums. append(nums, 5) ignores the returned slice. nums.append(5) uses invalid method syntax. nums += 5 is invalid for slices.

2. Final Answer:

   nums = append(nums, 5) -> Option D

3. Quick Check:

   append returns new slice, assign it [OK]

Hint: Always assign append result back to slice variable [OK]

Common Mistakes:

• Not assigning append result back
• Using method syntax like nums.append()
• Trying to add with += operator

3. What is the output of this Go code?

nums := []int{1, 2, 3, 4, 5}
slice := nums[1:4]
slice[0] = 10
fmt.Println(nums)

medium

A. [1 10 3 4 5]

B. [1 2 10 4 5]

C. [10 2 3 4 5]

D. [1 2 3 4 5]

Solution

1. Step 1: Understand slice referencing

   The slice slice := nums[1:4] references the original array elements at indexes 1, 2, and 3. Changing slice[0] to 10 changes nums[1] because slices share the underlying array. Output: [1 10 3 4 5]

2. Final Answer:

   [1 10 3 4 5] -> Option A

3. Quick Check:

   Slices share array, modifying slice changes original [OK]

Hint: Changing slice elements changes original array too [OK]

Common Mistakes:

• Thinking slice is a copy, not a reference
• Modifying wrong index in slice
• Confusing slice length with capacity

4. Identify the error in this Go code snippet:

nums := []int{1, 2, 3}
newSlice := nums[1:4]
fmt.Println(newSlice)

medium

A. Cannot print a slice directly with fmt.Println.

B. Syntax error in slice declaration.

C. Slicing beyond the slice length causes a runtime panic.

D. Missing import for fmt package.

Solution

1. Step 1: Check slice bounds

   The original slice nums has length 3, so valid indices are 0 to 2. Attempting nums[1:4] tries to access index 3 which is out of range, causing a runtime panic.

2. Final Answer:

   Slicing beyond the slice length causes a runtime panic. -> Option C

3. Quick Check:

   Slice end index must be ≤ length [OK]

Hint: Slice end index cannot exceed slice length [OK]

Common Mistakes:

• Assuming slice auto-expands
• Confusing compile error with runtime panic
• Ignoring slice length when slicing

5. Given a slice data := []int{2, 4, 6, 8, 10, 12}, how can you create a new slice containing only the even numbers greater than 6 using slicing and append?

hard

A. newSlice := data[2:5]

B. newSlice := append([]int{}, data[3:]...)

C. newSlice := append(data[:3], data[4:]...)

D. newSlice := data[3:len(data)]

Solution

1. Step 1: Identify elements > 6

   Elements greater than 6 are 8, 10, 12 at indexes 3, 4, 5. Using data[3:] gets these elements. To create a new slice (not referencing original), append to empty slice: newSlice := append([]int{}, data[3:]...).

2. Final Answer:

   newSlice := append([]int{}, data[3:]...) -> Option B

3. Quick Check:

   Slice and append to copy subset [OK]

Hint: Use append to copy slice subset safely [OK]

Common Mistakes:

• Using slice without append copies reference
• Incorrect slice indexes for desired elements
• Trying to remove elements by slicing incorrectly