Appending to slices in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Appending elements to a slice

What is the output of this Go program?

Go

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

A [1 2 3 4 5]

B [1 2 3]

C [4 5]

D Compilation error

💡 Hint

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

The append function adds the elements 4 and 5 to the slice s, resulting in [1 2 3 4 5].

❓ Predict Output

intermediate

Appending one slice to another

What will be printed by this Go program?

Go

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

A Runtime panic

B [1 2 [3 4]]

C [3 4 1 2]

D [1 2 3 4]

💡 Hint

Use the ... operator to append all elements of one slice to another.

The append function with b... appends all elements of b to a, resulting in [1 2 3 4].

❓ Predict Output

advanced

Appending to nil slice

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    var s []int
    s = append(s, 10)
    fmt.Println(s)
}

A [10]

B nil

C []

D Compilation error

💡 Hint

Appending to a nil slice creates a new slice with the appended elements.

Appending to a nil slice works fine and results in a slice with the new element.

❓ Predict Output

advanced

Appending inside a loop and slice capacity

What will be the output of this Go program?

Go

package main
import "fmt"
func main() {
    s := make([]int, 0, 2)
    for i := 1; i <= 3; i++ {
        s = append(s, i)
        fmt.Printf("len=%d cap=%d slice=%v\n", len(s), cap(s), s)
    }
}

A

len=1 cap=2 slice=[1]
len=2 cap=2 slice=[1 2]
len=3 cap=2 slice=[1 2 3]

B

len=1 cap=2 slice=[1]
len=2 cap=2 slice=[1 2]
len=3 cap=4 slice=[1 2 3]

C

len=1 cap=1 slice=[1]
len=2 cap=2 slice=[1 2]
len=3 cap=3 slice=[1 2 3]

D

len=1 cap=2 slice=[1]
len=2 cap=4 slice=[1 2]
len=3 cap=8 slice=[1 2 3]

💡 Hint

Slice capacity doubles when exceeded during append.

The slice starts with capacity 2. When the third element is appended, capacity grows to 4.

🧠 Conceptual

expert

Understanding slice append and underlying array sharing

Consider this Go code snippet. What will be the output? package main import "fmt" func main() { s1 := []int{1, 2, 3} s2 := s1[:2] s2 = append(s2, 4) fmt.Println("s1:", s1) fmt.Println("s2:", s2) }

A Runtime panic: index out of range

B

s1: [1 2 3]
s2: [1 2 4]

C

s1: [1 2 4]
s2: [1 2 4]

D

s1: [1 2 3]
s2: [1 2 3 4]

💡 Hint

Appending to s2 modifies the underlying array shared with s1 if capacity allows.

s2 is a slice of s1 with length 2 but capacity 3. Appending 4 modifies the shared array, changing s1's third element.