Array Access and Update at Index in DSA Go - Build from Scratch

Array Access and Update at Index

📖 Scenario: You are managing a list of daily temperatures recorded in a week. You want to check and update the temperature for a specific day.

🎯 Goal: Build a program that creates an array of temperatures, sets a specific day index, updates the temperature at that index, and prints the updated array.

📋 What You'll Learn

Create an array called temperatures with these exact values: 20, 22, 19, 24, 21, 23, 20

Create a variable called dayIndex and set it to 3

Update the temperature at dayIndex in temperatures to 25

Print the temperatures array after the update

💡 Why This Matters

🌍 Real World

Arrays are used to store collections of data like daily temperatures, stock prices, or sensor readings where you need quick access and updates by position.

💼 Career

Understanding how to access and update array elements is fundamental for software development, data processing, and working with any ordered data in programming.

1

Create the temperatures array

Create an array called temperatures with these exact values: 20, 22, 19, 24, 21, 23, 20

DSA Go

# Create the temperatures array with the given values
# Your code here

Hint

Use Go array syntax with fixed size 7 and initialize with the given values.

2

Set the day index

Create a variable called dayIndex and set it to 3

DSA Go

package main

func main() {
    temperatures := [7]int{20, 22, 19, 24, 21, 23, 20}
    
    // Create dayIndex variable and set it to 3
    // Your code here
}

Hint

Use := to declare and assign dayIndex in one line.

3

Update the temperature at the day index

Update the temperature at dayIndex in temperatures to 25

DSA Go

package main

func main() {
    temperatures := [7]int{20, 22, 19, 24, 21, 23, 20}
    dayIndex := 3

    // Update the temperature at dayIndex to 25
    // Your code here
}

Hint

Use array indexing with dayIndex to assign the new value.

4

Print the updated temperatures array

Print the temperatures array after the update using fmt.Println(temperatures)

DSA Go

package main

import "fmt"

func main() {
    temperatures := [7]int{20, 22, 19, 24, 21, 23, 20}
    dayIndex := 3
    temperatures[dayIndex] = 25

    // Print the updated temperatures array
    // Your code here
}

Hint

Import the fmt package and use fmt.Println to print the array.

Practice

1. What does the expression arr[2] do in an array arr?

easy

A. Accesses the element at index 3 of the array

B. Accesses the element at index 2 of the array

C. Updates the element at index 2 of the array

D. Deletes the element at index 2 of the array

Solution

1. Step 1: Understand array indexing

   Array indexing starts at 0, so index 2 means the third element.

2. Step 2: Identify the operation

   Using arr[2] accesses (reads) the element at index 2 without changing it.

3. Final Answer:

   Accesses the element at index 2 of the array -> Option B

4. Quick Check:

   arr[2] reads element at index 2 [OK]

Hint: Remember arrays start at 0 index [OK]

Common Mistakes:

• Thinking index 2 is the second element
• Confusing access with update
• Assuming indexing starts at 1

2. Which of the following is the correct syntax to update the element at index 1 in a Go array named nums to 10?

easy

A. nums[1] = 10

B. nums(1) = 10

C. nums[1] := 10

D. nums.update(1, 10)

Solution

1. Step 1: Recall Go array update syntax

   In Go, to update an element, use array[index] = value.

2. Step 2: Check each option

   nums[1] = 10 uses correct syntax. nums(1) = 10 uses parentheses which is invalid. nums[1] := 10 uses := which is for declaration, not update. nums.update(1, 10) uses a method that does not exist.

3. Final Answer:

   nums[1] = 10 -> Option A

4. Quick Check:

   Use square brackets and = for update [OK]

Hint: Use square brackets and = to update array element [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Using := instead of = for update
• Assuming arrays have update methods

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

package main
import "fmt"
func main() {
  arr := [4]int{5, 10, 15, 20}
  arr[2] = 25
  fmt.Println(arr)
}

medium

A. [5 10 25 20]

B. [5 10 15 20]

C. [25 10 15 20]

D. [5 25 15 20]

Solution

1. Step 1: Understand initial array and update

   Initial array is [5, 10, 15, 20]. The code updates element at index 2 (third element) to 25.

2. Step 2: Apply the update and print

   After update, array becomes [5, 10, 25, 20]. Printing shows this updated array.

3. Final Answer:

   [5 10 25 20] -> Option A

4. Quick Check:

   Index 2 updated to 25 [OK]

Hint: Index 2 means third element update [OK]

Common Mistakes:

• Confusing index 2 with index 1 or 3
• Not updating the array before print
• Expecting commas in printed array

4. Identify the error in the following Go code snippet:

package main
func main() {
  arr := [3]int{1, 2, 3}
  arr[3] = 4
}

medium

A. Cannot assign to arr[3] because arrays are immutable

B. Syntax error due to missing import

C. Index out of range error at arr[3]

D. No error, code runs fine

Solution

1. Step 1: Check array size and index used

   Array has size 3 with valid indices 0, 1, 2. Accessing arr[3] is invalid.

2. Step 2: Identify error type

   Accessing arr[3] causes runtime panic: index out of range error.

3. Final Answer:

   Index out of range error at arr[3] -> Option C

4. Quick Check:

   Index must be less than array length [OK]

Hint: Array indices go from 0 to length-1 [OK]

Common Mistakes:

• Assuming arr[3] is valid for size 3 array
• Thinking arrays are immutable in Go
• Ignoring runtime errors

5. Given an array arr := [5]int{1, 2, 3, 4, 5}, which code snippet correctly doubles the value at each index using array access and update?

hard

A. for i := 1; i <= len(arr); i++ { arr[i] = arr[i] * 2 }

B. for i := 0; i < len(arr); i++ { arr[i] *= 2; arr[i+1] = arr[i] }

C. for i := 0; i < len(arr); i++ { arr[i+1] = arr[i] * 2 }

D. for i := 0; i < len(arr); i++ { arr[i] = arr[i] * 2 }

Solution

1. Step 1: Understand array length and valid indices

   Array length is 5, valid indices are 0 to 4. Loop must run from 0 to 4.

2. Step 2: Analyze each loop snippet

   for i := 0; i < len(arr); i++ { arr[i] = arr[i] * 2 } loops correctly and updates each element by doubling. for i := 1; i <= len(arr); i++ { arr[i] = arr[i] * 2 } uses i from 1 to 5, arr[5] is invalid index. for i := 0; i < len(arr); i++ { arr[i+1] = arr[i] * 2 } updates arr[i+1], which causes out of range at last iteration. for i := 0; i < len(arr); i++ { arr[i] *= 2; arr[i+1] = arr[i] } updates arr[i+1] inside loop, causing out of range and incorrect logic.

3. Final Answer:

   for i := 0; i < len(arr); i++ { arr[i] = arr[i] * 2 } -> Option D

4. Quick Check:

   Loop from 0 to len-1 and update arr[i] [OK]

Hint: Loop indices 0 to len-1 for safe access [OK]

Common Mistakes:

• Looping beyond array length causing index error
• Updating wrong indices inside loop
• Using <= instead of < in loop condition