Slice and array relationship in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a slice from the array named arr.

Go

arr := [5]int{1, 2, 3, 4, 5}
slice := arr[1]

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

A[:3]

B[3:]

C[1:4]

D[5:]

Attempts:

3 left

💡 Hint

Common Mistakes

Using an empty slice like [5:] results in an empty slice, not an error.

Confusing slice indices and array indices.

The slice arr[:3] creates a slice of the first three elements from the array arr.

2fill in blank

medium

Complete the code to append the value 6 to the slice named slice.

Go

slice := []int{1, 2, 3}
slice = append(slice, [1])

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

A6

B5

C7

D8

Attempts:

3 left

💡 Hint

Common Mistakes

Appending a wrong number changes the slice content unexpectedly.

Forgetting to assign the result of append back to the slice.

Appending 6 to the slice adds the value 6 as the last element.

3fill in blank

hard

Fix the error in the code to correctly create a slice from the array arr.

Go

arr := [4]int{10, 20, 30, 40}
slice := arr[1]

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

A[1:5]

B[2:6]

C[0:4]

D[4:4]

Attempts:

3 left

💡 Hint

Common Mistakes

Using an upper index greater than the array length causes runtime panic.

Using an empty slice like [4:4] results in an empty slice, not an error.

The slice arr[0:4] correctly slices all elements from index 0 up to but not including 4, which is the array length.

4fill in blank

hard

Fill both blanks to create a slice of the middle three elements from the array arr.

Go

arr := [5]int{5, 10, 15, 20, 25}
slice := arr[1][2]

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

A[1:

B2]

C4]

D[2:

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect indices that include too few or too many elements.

Forgetting that the end index is not included in the slice.

The slice arr[1:4] selects elements at indices 1, 2, and 3, which are the middle three elements.

5fill in blank

hard

Fill all three blanks to create a new slice from arr and append the value 100.

Go

arr := [4]int{1, 2, 3, 4}
slice := append(arr[1][2], [3])

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

A[1:

B3]

C100

D[0:

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong slice indices that cause runtime errors.

Appending a value without assigning back to the slice.

The code arr[1:3] creates a slice with elements at indices 1 and 2, then appends 100 to it.

Practice

1. In Go, what is the relationship between a slice and the underlying array it references?

easy

A. A slice is a completely independent copy of the array.

B. A slice is a view into an array and shares the same data.

C. A slice stores data separately and does not affect the array.

D. A slice can only reference arrays of fixed size 10.

Solution

1. Step 1: Understand slice basics

   A slice in Go points to an underlying array and does not copy data.

2. Step 2: Relationship between slice and array

   Changes to the slice affect the array and vice versa because they share the same data.

3. Final Answer:

   A slice is a view into an array and shares the same data. -> Option B

4. Quick Check:

   Slice shares array data = B [OK]

Hint: Remember: slices share data with arrays, not copy it [OK]

Common Mistakes:

• Thinking slices copy array data
• Believing slices are independent arrays
• Assuming slices have fixed size

2. Which of the following is the correct way to create a slice from an array arr := [5]int{1,2,3,4,5} that includes elements 2, 3, and 4?

easy

A. slice := arr[1:4]

B. slice := arr[2:5]

C. slice := arr[0:3]

D. slice := arr[3:6]

Solution

1. Step 1: Identify slice indices

   Slice syntax is arr[start:end], including start but excluding end index.

2. Step 2: Select correct indices for elements 2,3,4

   Elements 2,3,4 are at indices 1,2,3, so slice is arr[1:4].

3. Final Answer:

   slice := arr[1:4] -> Option A

4. Quick Check:

   Slice indices 1 to 4 exclude 4 = D [OK]

Hint: Slice includes start index, excludes end index [OK]

Common Mistakes:

• Using wrong start or end index
• Trying to slice beyond array length
• Confusing inclusive/exclusive slice bounds

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

arr := [3]int{10, 20, 30}
slice := arr[:]
slice[1] = 99
fmt.Println(arr)

medium

A. [99 20 30]

B. [10 20 30]

C. [10 99 30]

D. [10 20 99]

Solution

1. Step 1: Understand slice referencing

   slice := arr[:] creates a slice referencing the entire array.

2. Step 2: Modify slice element

   slice[1] = 99 changes the second element of the slice and underlying array.

3. Step 3: Print array

   Printing arr shows the updated array: [10 99 30].

4. Final Answer:

   [10 99 30] -> Option C

5. Quick Check:

   Slice change affects array = A [OK]

Hint: Changing slice changes array too [OK]

Common Mistakes:

• Assuming array stays unchanged
• Confusing slice copy with reference
• Misreading slice syntax

4. Identify the error in the following Go code snippet:

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

medium

A. No error, output is [1 2 10 4]

B. Syntax error in slice declaration

C. Array length mismatch error

D. Index out of range error when assigning to slice[2]

Solution

1. Step 1: Check slice length

   slice := arr[1:3] includes elements at indices 1 and 2, length 2.

2. Step 2: Accessing slice[2]

   slice[2] tries to access third element (index 2), which is out of range.

3. Final Answer:

   Index out of range error when assigning to slice[2] -> Option D

4. Quick Check:

   Slice length 2, index 2 invalid = C [OK]

Hint: Slice length limits valid indices from 0 to len-1 [OK]

Common Mistakes:

• Assuming slice length equals array length
• Using invalid slice indices
• Ignoring runtime panics

5. Given the array arr := [5]int{1, 2, 3, 4, 5}, you create two slices:
slice1 := arr[1:4]
slice2 := arr[2:5]
If you set slice1[1] = 99, what will be the content of slice2?

hard

A. [99 4 5]

B. [3 99 5]

C. [3 4 5]

D. [2 99 5]

Solution

1. Step 1: Identify slice1 and slice2 elements

   slice1 = arr[1:4] = elements at indices 1,2,3 -> [2,3,4]
   slice2 = arr[2:5] = elements at indices 2,3,4 -> [3,4,5]

2. Step 2: Modify slice1[1]

   slice1[1] is element at arr index 2 (value 3), changed to 99.
   So arr becomes [1,2,99,4,5].

3. Step 3: Check slice2 after modification

   slice2 references arr[2], arr[3], arr[4] -> [99,4,5].

4. Final Answer:

   [99 4 5] -> Option A

5. Quick Check:

   Shared array data means slice2 reflects change = B [OK]

Hint: Slices share array; changing one affects overlapping slices [OK]

Common Mistakes:

• Mixing up slice indices and values
• Forgetting slices share underlying array
• Assuming slices are independent copies