Why arrays are needed in Go - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of array initialization and access

What is the output of this Go program that initializes an array and prints its elements?

Go

package main
import "fmt"
func main() {
    var arr [3]int = [3]int{10, 20, 30}
    for i := 0; i < len(arr); i++ {
        fmt.Print(arr[i], " ")
    }
}

A 10 20 30

B 10 20 30 0

C 0 0 0

D Compilation error

💡 Hint

Remember arrays hold fixed-size collections of elements of the same type.

The array is initialized with values 10, 20, 30. The loop prints each element separated by space, so output is '10 20 30 '.

🧠 Conceptual

intermediate

Why use arrays instead of separate variables?

Why are arrays useful compared to using many separate variables for similar data?

A Arrays automatically sort the data for you.

B Arrays allow grouping multiple values of the same type under one name for easy management.

C Arrays use less memory than separate variables.

D Arrays can store different types of data in one variable.

💡 Hint

Think about how you handle many similar items in real life, like a row of mailboxes.

Arrays let you keep many values together under one name, making it easier to store, access, and manage related data.

❓ Predict Output

advanced

Output when modifying array elements

What is the output of this Go program that modifies an array element?

Go

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

A [1 2 10 4]

B [1 2 3 4]

C [10 2 3 4]

D Runtime error

💡 Hint

Arrays allow changing values at specific positions by index.

The element at index 2 (third element) is changed from 3 to 10, so the array prints as [1 2 10 4].

🔧 Debug

advanced

Identify the error in array declaration

What error does this Go code produce and why?

Go

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

A no error, compiles fine

B index out of range error

C syntax error: missing colon

D cannot use [4]int literal as [3]int value in assignment

💡 Hint

Check if the array sizes on both sides match.

The variable arr is declared as an array of size 3 but assigned an array literal of size 4, causing a type mismatch error.

🚀 Application

expert

Count how many elements in an array are greater than 5

What is the value of count after running this Go code?

Go

package main
import "fmt"
func main() {
    arr := [5]int{3, 7, 2, 9, 5}
    count := 0
    for _, v := range arr {
        if v > 5 {
            count++
        }
    }
    fmt.Println(count)
}

A 3

B 1

C 2

D 0

💡 Hint

Look at each element and count only those greater than 5.

Only 7 and 9 are greater than 5, so count is 2.

Practice

1. Why do we need arrays in Go programming?

easy

A. To store multiple values of the same type together in one variable

B. To store only one value at a time

C. To perform mathematical calculations faster

D. To create functions that run automatically

Solution

1. Step 1: Understand the purpose of arrays

   Arrays allow storing many values of the same type in one place, making it easier to manage related data.

2. Step 2: Compare options with array purpose

   Only To store multiple values of the same type together in one variable correctly describes storing multiple values together; others describe unrelated concepts.

3. Final Answer:

   To store multiple values of the same type together in one variable -> Option A

4. Quick Check:

   Arrays store multiple values = A [OK]

Hint: Arrays hold many same-type items in one variable [OK]

Common Mistakes:

• Thinking arrays store different types together
• Confusing arrays with single variables
• Assuming arrays speed up math automatically

2. Which of the following is the correct way to declare an array of 3 integers in Go?

easy

A. var arr [3]int

B. arr := []int{3}

C. var arr int[3]

D. arr = array(3)int

Solution

1. Step 1: Recall Go array declaration syntax

   In Go, arrays are declared with var name [size]type, for example var arr [3]int.

2. Step 2: Check each option

   var arr [3]int matches correct syntax. arr := []int{3} is a slice, not an array. Options A and D are invalid syntax.

3. Final Answer:

   var arr [3]int -> Option A

4. Quick Check:

   Array declaration uses var name [size]type = C [OK]

Hint: Remember: var name [size]type declares an array [OK]

Common Mistakes:

• Using slice syntax instead of array syntax
• Placing size after type incorrectly
• Using non-Go keywords like 'array'

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

package main
import "fmt"
func main() {
  var nums [3]int
  nums[0] = 10
  nums[1] = 20
  nums[2] = 30
  fmt.Println(nums[1])
}

medium

A. 10

B. 0

C. 20

D. 30

Solution

1. Step 1: Understand array indexing

   Arrays in Go start at index 0. nums[1] refers to the second element.

2. Step 2: Check assigned values

   nums[1] was assigned 20, so printing nums[1] outputs 20.

3. Final Answer:

   20 -> Option C

4. Quick Check:

   nums[1] = 20, output = 20 [OK]

Hint: Remember Go arrays start at index 0 [OK]

Common Mistakes:

• Confusing index 1 with index 0
• Assuming default zero value prints instead
• Mixing up assigned values

4. Find the error in this Go code that uses an array:

package main
import "fmt"
func main() {
  var arr [2]int
  arr[2] = 5
  fmt.Println(arr)
}

medium

A. Missing import statement

B. Print statement syntax error

C. Incorrect array declaration syntax

D. Array size is too small for index 2

Solution

1. Step 1: Check array size and index used

   The array arr has size 2, so valid indexes are 0 and 1 only.

2. Step 2: Identify invalid index usage

   Accessing arr[2] is out of bounds and causes a runtime error.

3. Final Answer:

   Array size is too small for index 2 -> Option D

4. Quick Check:

   Index 2 invalid for size 2 array = B [OK]

Hint: Array indexes go from 0 to size-1 only [OK]

Common Mistakes:

• Using index equal to array size
• Ignoring runtime index errors
• Thinking import or print cause error

5. You want to store the daily temperatures for a week in Go. Which is the best reason to use an array for this?

hard

A. Because arrays automatically sort the temperatures for you

B. Because the number of days is fixed and you want to access temperatures by day index

C. Because arrays can grow dynamically as you add more days

D. Because arrays allow storing different types like int and string together

Solution

1. Step 1: Understand the problem context

   Daily temperatures for a week means exactly 7 values, fixed size, accessed by day position.

2. Step 2: Match array properties to the need

   Arrays have fixed size and allow access by index, perfect for fixed-length daily data.

3. Step 3: Eliminate incorrect options

   Arrays do not sort automatically, cannot grow dynamically, and store only one type.

4. Final Answer:

   Because the number of days is fixed and you want to access temperatures by day index -> Option B

5. Quick Check:

   Fixed size + index access = A [OK]

Hint: Use arrays when size is fixed and order matters [OK]

Common Mistakes:

• Thinking arrays grow dynamically
• Assuming arrays sort data automatically
• Believing arrays hold mixed types