Accessing array elements in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing array element by index

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    arr := [4]int{10, 20, 30, 40}
    fmt.Println(arr[2])
}

A 20

B 40

C 30

D Index out of range error

💡 Hint

Remember that Go arrays are zero-indexed, so the first element is at index 0.

The array has elements 10, 20, 30, 40 at indices 0, 1, 2, 3 respectively. Accessing arr[2] returns 30.

❓ Predict Output

intermediate

Accessing last element of an array

What will this Go program print?

Go

package main
import "fmt"
func main() {
    arr := [5]string{"a", "b", "c", "d", "e"}
    fmt.Println(arr[len(arr)-1])
}

A e

B a

C d

D Index out of range error

💡 Hint

len(arr) gives the number of elements. The last index is length minus one.

The last element is at index 4 (5-1), which is "e".

❓ Predict Output

advanced

What error occurs when accessing out-of-bounds index?

What error does this Go program produce when run?

Go

package main
func main() {
    arr := [3]int{1, 2, 3}
    _ = arr[3]
}

A no error, prints 0

B panic: runtime error: index out of range [3] with length 3

C compile error: invalid array index

D panic: nil pointer dereference

💡 Hint

Array indices must be within 0 to length-1. Accessing index 3 in a 3-element array is invalid.

Go panics at runtime with an index out of range error when accessing arr[3].

🧠 Conceptual

advanced

Understanding array element access with variables

What is the output of this Go program?

Go

package main
import "fmt"
func main() {
    arr := [3]int{5, 10, 15}
    i := 1
    fmt.Println(arr[i])
    i = 2
    fmt.Println(arr[i])
}

A 15\n10

B 5\n10

C runtime error: index out of range

D 10\n15

💡 Hint

The variable i changes before the second print, so the index changes.

First print accesses arr[1] which is 10, second print accesses arr[2] which is 15.

🔧 Debug

expert

Identify the cause of the runtime error

This Go program crashes with a runtime error. What is the cause?

Go

package main
import "fmt"
func main() {
    arr := [2]int{7, 8}
    for i := 0; i <= len(arr); i++ {
        fmt.Println(arr[i])
    }
}

A The loop condition uses <= instead of < causing out-of-bounds access

B Array is not initialized properly

C fmt.Println cannot print array elements

D Variable i is not declared

💡 Hint

Check the loop boundary and valid indices for the array.

The loop runs from i=0 to i=2 inclusive, but arr has length 2, so arr[2] is out of range causing runtime panic.