Array Insertion at End in DSA Go - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after inserting elements at the end of the array?

Consider the following Go code that inserts elements at the end of an array (slice). What will be printed?

DSA Go

package main
import "fmt"
func main() {
    arr := []int{1, 2, 3}
    arr = append(arr, 4)
    arr = append(arr, 5)
    fmt.Println(arr)
}

A [1 2 3 4]

B [1 2 3 4 5]

C [4 5]

D [1 2 3]

💡 Hint

Remember that append adds elements to the end of the slice and returns the new slice.

The append function adds elements to the end of the slice. Starting with [1 2 3], appending 4 and then 5 results in [1 2 3 4 5].

❓ Predict Output

intermediate

What is the length of the array after insertions?

Given the following Go code, what is the length of the slice after all insertions?

DSA Go

package main
import "fmt"
func main() {
    arr := []int{10, 20}
    arr = append(arr, 30)
    arr = append(arr, 40, 50)
    fmt.Println(len(arr))
}

A 2

B 4

C 3

D 5

💡 Hint

Count the initial elements and all appended elements.

Initial slice has 2 elements. Appending 30 adds 1 element, then appending 40 and 50 adds 2 more. Total length is 2 + 1 + 2 = 5.

❓ Predict Output

advanced

What is the output of this slice insertion and print?

Analyze the Go code below. What will be printed?

DSA Go

package main
import "fmt"
func main() {
    arr := make([]int, 3)
    arr[0] = 7
    arr[1] = 8
    arr[2] = 9
    arr = append(arr, 10)
    fmt.Println(arr)
}

A [7 8 9 10]

B [0 0 0 10]

C [7 8 9]

D [10]

💡 Hint

Remember make creates a slice with zero values initially.

make([]int, 3) creates a slice of length 3 with zeros. We assign values 7,8,9 to indices 0,1,2. Then append 10 adds it at the end. So output is [7 8 9 10].

❓ Predict Output

advanced

What error occurs when appending to a nil slice?

What will happen when running this Go code?

DSA Go

package main
import "fmt"
func main() {
    var arr []int
    arr = append(arr, 1)
    fmt.Println(arr)
}

A [1]

B panic: runtime error: index out of range

C nil

D compile error

💡 Hint

Appending to a nil slice is allowed in Go.

In Go, appending to a nil slice creates a new slice with the appended element. So the output is [1].

🧠 Conceptual

expert

What is the capacity of the slice after multiple append operations?

Given this Go code, what is the capacity of the slice after all append operations?

DSA Go

package main
import "fmt"
func main() {
    arr := make([]int, 0, 2)
    arr = append(arr, 1)
    arr = append(arr, 2)
    arr = append(arr, 3)
    fmt.Println(cap(arr))
}

A 1

B 2

C 4

D 3

💡 Hint

When capacity is exceeded, Go doubles the capacity.

Initial capacity is 2. After appending 3 elements, capacity grows to 4 (doubled from 2).

Practice

1. What happens when you insert an element at the end of a fixed-size array in Go?

easy

A. You cannot insert because arrays have fixed size

B. The element replaces the first element

C. The element is added and array size increases automatically

D. The array is converted to a slice automatically

Solution

1. Step 1: Understand Go array size

   Arrays in Go have a fixed size defined at declaration and cannot grow.

2. Step 2: Effect of insertion at end

   Since size is fixed, you cannot add new elements beyond the declared size.

3. Final Answer:

   You cannot insert because arrays have fixed size -> Option A

4. Quick Check:

   Fixed size array = no insertion beyond size [OK]

Hint: Arrays have fixed size; no automatic growth on insertion [OK]

Common Mistakes:

• Thinking arrays can grow automatically
• Confusing arrays with slices
• Assuming insertion replaces last element

2. Which of the following is the correct way to append an element 10 to a slice named nums in Go?

easy

A. nums = nums + 10

B. nums.append(10)

C. append(nums, 10)

D. nums = append(nums, 10)

Solution

1. Step 1: Recall Go slice append syntax

   In Go, append returns a new slice with the element added, so assignment is needed.

2. Step 2: Check each option

   nums = append(nums, 10) correctly assigns the result of append to nums. Others are invalid syntax or missing assignment.

3. Final Answer:

   nums = append(nums, 10) -> Option D

4. Quick Check:

   Use append with assignment to add element [OK]

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

Common Mistakes:

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

3. What is the output of the following Go code?

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

medium

A. [1 2 3]

B. [4 1 2 3]

C. [1 2 3 4]

D. Compilation error

Solution

1. Step 1: Understand initial slice and append

   nums starts as [1 2 3]. append(nums, 4) adds 4 at the end.

2. Step 2: Print the updated slice

   After append, nums becomes [1 2 3 4], which is printed.

3. Final Answer:

   [1 2 3 4] -> Option C

4. Quick Check:

   Appending 4 adds it at end [OK]

Hint: append adds element at end, print shows updated slice [OK]

Common Mistakes:

• Expecting original slice without new element
• Thinking append adds at start
• Confusing slice with array syntax

4. Identify the error in the following Go code that tries to insert 5 at the end of an array:

arr := [3]int{1, 2, 3}
arr = append(arr, 5)
fmt.Println(arr)

medium

A. Cannot use append on array; append works only on slices

B. Array size is too small; must declare larger array

C. Missing import for fmt package

D. Syntax error in array declaration

Solution

1. Step 1: Check type of arr

   arr is declared as an array [3]int, which has fixed size and no append method.

2. Step 2: Understand append usage

   append works only on slices, not arrays. Using append on array causes error.

3. Final Answer:

   Cannot use append on array; append works only on slices -> Option A

4. Quick Check:

   append requires slice, not array [OK]

Hint: append works only on slices, not fixed-size arrays [OK]

Common Mistakes:

• Trying to append to fixed-size array
• Ignoring difference between array and slice
• Assuming append auto-converts array to slice

5. Given a slice data := []int{2, 4, 6}, which code snippet correctly inserts the value 8 at the end and then doubles all elements?

hard

A. data = append(data, 8)
for _, v := range data {
v *= 2
}
fmt.Println(data)

B. data = append(data, 8)
for i := range data {
data[i] *= 2
}
fmt.Println(data)

C. data = append(data, 8)
for i := 0; i < len(data); i++ {
data[i] = data[i] + 2
}
fmt.Println(data)

D. data = append(data, 8)
for i := range data {
data[i] = data[i] / 2
}
fmt.Println(data)

Solution

1. Step 1: Append 8 to slice

   data = append(data, 8) adds 8 at the end, making data [2 4 6 8].

2. Step 2: Double each element correctly

   Using for i := range data and data[i] *= 2 doubles each element in place.

3. Step 3: Check other options

   data = append(data, 8) for _, v := range data { v *= 2 } fmt.Println(data) doubles copy of value, not original slice. Options C and D do wrong math.

4. Final Answer:

   data = append(data, 8) for i := range data { data[i] *= 2 } fmt.Println(data) -> Option B

5. Quick Check:

   Append then modify elements by index [OK]

Hint: Modify slice elements by index, not by value copy [OK]

Common Mistakes:

• Modifying value copy in range instead of slice element
• Using wrong arithmetic operation
• Not assigning append result back