Slicing operations in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of slice length and capacity

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    s := make([]int, 3, 5)
    fmt.Println(len(s), cap(s))
}

A 5 3

B 3 5

C 0 3

D 3 3

💡 Hint

Remember len returns the number of elements, cap returns the capacity.

The slice s is created with length 3 and capacity 5, so len(s) is 3 and cap(s) is 5.

❓ Predict Output

intermediate

Result of slicing a slice

What will be printed by this Go program?

Go

package main
import "fmt"
func main() {
    arr := []int{10, 20, 30, 40, 50}
    s := arr[1:4]
    fmt.Println(s)
}

A [30 40 50]

B [10 20 30]

C [20 30 40 50]

D [20 30 40]

💡 Hint

Slice from index 1 up to but not including 4.

Slicing arr[1:4] includes elements at indices 1, 2, and 3: 20, 30, 40.

❓ Predict Output

advanced

Effect of modifying a slice on the underlying array

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    arr := [3]int{1, 2, 3}
    s := arr[:]
    s[1] = 20
    fmt.Println(arr)
}

A [1 20 3]

B [1 2 3]

C [20 2 3]

D [1 20 20]

💡 Hint

Slices share the underlying array with the original array.

Modifying s[1] changes arr[1] because s references the same array.

❓ Predict Output

advanced

Capacity after slicing with full slice expression

What will this program print?

Go

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

A 2 4

B 3 4

C 2 3

D 3 3

💡 Hint

Capacity is calculated as max - start index in full slice expression.

Length is 3-1=2, capacity is 4-1=3.

❓ Predict Output

expert

Output after appending to a slice and modifying original array

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    arr := []int{1, 2, 3}
    s := arr[0:2:2]
    s = append(s, 4)
    arr[0] = 10
    fmt.Println(s, arr)
}

A [1 2 4] [10 2 3]

B [10 2 4] [10 2 3]

C [1 2 4] [1 2 3]

D [10 2 3] [10 2 3]

💡 Hint

Appending may create a new underlying array if capacity is exceeded.

Appending 4 to s creates a new array for s, so modifying arr[0] affects arr but not s's first element.