Slice length and capacity in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a slice with length 3.

Go

s := make([]int, [1])
fmt.Println(len(s))

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

A5

B0

C3

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using capacity instead of length in the make function.

Confusing length with capacity.

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 create a slice with length 3 and capacity 5.

Go

s := make([]int, 3, [1])
fmt.Println(cap(s))

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

A0

B10

C3

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Setting capacity smaller than length causes a compile error.

Confusing length and capacity positions in make.

The third argument in make sets the capacity of the slice. Here, capacity 5 means the slice can grow up to 5 elements without reallocating.

3fill in blank

hard

Fix the error in the code to print the length of the slice.

Go

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

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

Acap

Blen

Csize

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using cap instead of len to get length.

Using non-existent functions like size or length.

The built-in function len returns the length of a slice in Go.

4fill in blank

hard

Fill both blanks to create a slice with length 2 and capacity 4, then print length and capacity.

Go

s := make([]int, [1], [2])
fmt.Println(len(s), cap(s))

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

A2

B3

C4

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping length and capacity values.

Setting capacity smaller than length.

The first blank is the length (2), and the second blank is the capacity (4). The make function uses these to create the slice.

5fill in blank

hard

Fill the blanks to create a slice from an array, then print its length and capacity.

Go

arr := [5]int{1, 2, 3, 4, 5}
s := arr[[1]:[2]]
fmt.Println(len(s), cap(s))

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

A1

B2

C5

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing slice length with capacity.

Using wrong indices for slicing.

The slice s starts at index 1 and ends before index 3, so length is 2. Capacity is from start index 1 to end of array index 5, so capacity is 4.

Practice

1. In Go, what does the len() function return when used on a slice?

easy

A. The maximum number of elements the slice can hold

B. The total memory size of the slice in bytes

C. The index of the last element in the slice

D. The number of elements currently in the slice

Solution

1. Step 1: Understand the purpose of len() on slices

   The len() function returns how many elements are currently stored in the slice.

2. Step 2: Differentiate from capacity

   Capacity is about how many elements the slice can hold before resizing, not the current count.

3. Final Answer:

   The number of elements currently in the slice -> Option D

4. Quick Check:

   len(slice) = current element count [OK]

Hint: Remember: len = current items, cap = max before grow [OK]

Common Mistakes:

• Confusing length with capacity
• Thinking len returns memory size
• Assuming len gives last index

2. Which of the following is the correct way to create a slice with length 3 and capacity 5 in Go?

easy

A. make([]int, 5, 3)

B. make([]int, 3, 5)

C. []int{3, 5}

D. make([]int, 3)

Solution

1. Step 1: Recall the make function signature for slices

   make([]T, length, capacity) creates a slice with given length and capacity.

2. Step 2: Match length and capacity values

   To get length 3 and capacity 5, use make([]int, 3, 5).

3. Final Answer:

   make([]int, 3, 5) -> Option B

4. Quick Check:

   make([]int, length, capacity) [OK]

Hint: make([]T, len, cap) sets length then capacity [OK]

Common Mistakes:

• Swapping length and capacity arguments
• Using slice literal instead of make
• Omitting capacity when needed

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

nums := make([]int, 2, 4)
nums[0] = 10
nums[1] = 20
fmt.Println(len(nums), cap(nums))

medium

A. 2 2

B. 0 4

C. 2 4

D. 4 4

Solution

1. Step 1: Analyze slice creation

   make([]int, 2, 4) creates a slice with length 2 and capacity 4.

2. Step 2: Check length and capacity after assignments

   Assigning values to existing indices does not change length or capacity.

3. Final Answer:

   2 4 -> Option C

4. Quick Check:

   len = 2, cap = 4 [OK]

Hint: Length stays same unless you append beyond capacity [OK]

Common Mistakes:

• Confusing length with capacity
• Assuming capacity equals length after assignment
• Thinking length changes when assigning values

4. Consider this code snippet:

arr := []int{1, 2, 3, 4, 5}
slice := arr[1:3]
fmt.Println(len(slice), cap(slice))

What is the correct output?

medium

A. 2 4

B. 2 2

C. 3 4

D. 3 5

Solution

1. Step 1: Determine length of the slice

   The slice is from index 1 to 3 (exclusive), so length = 3 - 1 = 2.

2. Step 2: Calculate capacity of the slice

   Capacity is from start index to end of original array: 5 - 1 = 4.

3. Final Answer:

   2 4 -> Option A

4. Quick Check:

   len = 2, cap = 4 from slice indices [OK]

Hint: Capacity = original array length - slice start index [OK]

Common Mistakes:

• Using slice length as capacity
• Confusing slice end index with capacity
• Assuming capacity equals original array length

5. You have a slice s := make([]int, 3, 5). You append two elements to it. What will be the length and capacity of s after these appends?

hard

A. Length 5, Capacity 5

B. Length 5, Capacity 10

C. Length 3, Capacity 5

D. Length 5, Capacity 6

Solution

1. Step 1: Understand initial slice size

   Slice s starts with length 3 and capacity 5.

2. Step 2: Append two elements within capacity

   Appending two elements increases length to 5, capacity remains 5 because it is not exceeded.

3. Final Answer:

   Length 5, Capacity 5 -> Option A

4. Quick Check:

   Appending within capacity keeps capacity same [OK]

Hint: Capacity grows only when length exceeds capacity [OK]

Common Mistakes:

• Assuming capacity doubles immediately after append
• Confusing length with capacity after append
• Thinking capacity increases by 1 per append