Array limitations in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a fixed size array in Go?

An array in Go has a fixed size defined at the time of declaration. This size cannot be changed later.

beginner

Can you resize an array in Go after it is created?

No, arrays in Go cannot be resized after creation. You must create a new array if you need a different size.

intermediate

What happens if you try to access an index outside the array bounds in Go?

Accessing an index outside the array bounds causes a runtime panic error, stopping the program.

intermediate

Why might arrays be less flexible than slices in Go?

Arrays have fixed size and cannot grow or shrink, while slices are dynamic and can change size.

intermediate

How does Go treat arrays when passed to functions?

Arrays are passed by value, meaning a copy is made. Changes inside the function do not affect the original array.

What is the size of an array in Go after it is declared?

A Fixed and cannot be changed

B Can be increased dynamically

C Can be decreased dynamically

D Depends on the number of elements added

Arrays in Go have a fixed size defined at declaration and cannot be resized.

What happens if you access an array index that is out of range in Go?

A Returns zero value silently

B Compiles with a warning

C Causes a runtime panic error

D Automatically resizes the array

Accessing out-of-range indexes causes a runtime panic error in Go.

How are arrays passed to functions in Go?

A By value (copy)

B By pointer automatically

C By reference

D They cannot be passed

Arrays are passed by value, meaning a copy is made when passed to functions.

Which Go type is more flexible than arrays for changing size?

A Map

B Slice

C Struct

D Channel

Slices are dynamic and can grow or shrink, unlike fixed-size arrays.

Can you change the length of an array after it is created in Go?

A Yes, using built-in functions

B Only if the array is a pointer

C Yes, by appending elements

D No, arrays have fixed length

Arrays have fixed length and cannot be changed after creation.

Explain the main limitations of arrays in Go and how they affect programming.

Think about size, passing behavior, and error handling.

Compare arrays and slices in Go focusing on their limitations and flexibility.

Consider size and how they behave when passed around.

Practice

1. Which statement best describes arrays in Go?

easy

A. Arrays can grow dynamically as elements are added.

B. Arrays automatically resize when elements are removed.

C. Arrays have a fixed size that cannot be changed after creation.

D. Arrays are the same as slices in Go.

Solution

1. Step 1: Understand array size behavior

   In Go, arrays have a fixed size defined when they are created and cannot be resized later.

2. Step 2: Compare with other options

   Options A and C describe dynamic resizing, which arrays do not support. Arrays are the same as slices in Go. is incorrect because arrays and slices are different types.

3. Final Answer:

   Arrays have a fixed size that cannot be changed after creation. -> Option C

4. Quick Check:

   Array size fixed = B [OK]

Hint: Remember: Go arrays have fixed size, slices are flexible [OK]

Common Mistakes:

• Confusing arrays with slices
• Thinking arrays can resize dynamically
• Assuming arrays and slices are identical

2. Which of the following is the correct way to declare an array of 5 integers in Go?

easy

A. var arr [5]int

B. arr := []int{5}

C. var arr []int = make([]int, 5)

D. arr := [int]5

Solution

1. Step 1: Identify correct array declaration syntax

   In Go, arrays are declared with the size inside square brackets before the type, like [5]int.

2. Step 2: Analyze other options

   arr := []int{5} declares a slice with one element 5, not an array of size 5. var arr []int = make([]int, 5) declares a slice using make, not an array. arr := [int]5 is invalid syntax.

3. Final Answer:

   var arr [5]int -> Option A

4. Quick Check:

   Array syntax = var arr [size]type [OK]

Hint: Array size goes inside brackets before type [OK]

Common Mistakes:

• Using slice syntax instead of array syntax
• Placing size after type
• Using make() for arrays

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

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

medium

A. 20

B. 10

C. runtime error

D. 0

Solution

1. Step 1: Understand default array values in Go

   Arrays in Go are initialized with zero values for their type. For int, the default is 0.

2. Step 2: Check assigned and unassigned elements

   arr[0] and arr[1] are set to 10 and 20. arr[2] is not assigned, so it remains 0.

3. Final Answer:

   0 -> Option D

4. Quick Check:

   Unassigned int array element = 0 [OK]

Hint: Unassigned int array elements default to 0 [OK]

Common Mistakes:

• Expecting unassigned elements to be garbage or error
• Confusing array with slice behavior
• Assuming runtime error for out-of-range access

4. What is wrong with this Go code snippet?

var arr [3]int
arr = append(arr, 4)

medium

A. The syntax is correct; no error.

B. Arrays cannot be appended to; append works only with slices.

C. append requires a pointer to the array.

D. The array size is too small for append.

Solution

1. Step 1: Understand append function usage

   In Go, append is used only with slices, not arrays.

2. Step 2: Identify error cause

   Trying to append to an array causes a compile-time error because arrays have fixed size and do not support append.

3. Final Answer:

   Arrays cannot be appended to; append works only with slices. -> Option B

4. Quick Check:

   append() works only with slices [OK]

Hint: Use slices, not arrays, with append() [OK]

Common Mistakes:

• Trying to append to arrays
• Assuming append resizes arrays
• Ignoring compile-time errors

5. You need a collection that can grow and shrink dynamically in Go. Which approach correctly solves this limitation of arrays?

hard

A. Use slices instead of arrays for flexible size.

B. Declare a very large array to hold all possible elements.

C. Manually copy array elements to a new larger array when needed.

D. Use a map with integer keys instead of an array.

Solution

1. Step 1: Identify the limitation of arrays

   Arrays have fixed size and cannot grow or shrink dynamically.

2. Step 2: Choose the flexible collection type

   Slices in Go provide dynamic resizing and are the recommended way to handle flexible collections.

3. Step 3: Evaluate other options

   Declare a very large array to hold all possible elements. wastes memory and is inflexible. Manually copy array elements to a new larger array when needed. is manual and error-prone. Use a map with integer keys instead of an array. changes data structure but not necessarily size flexibility.

4. Final Answer:

   Use slices instead of arrays for flexible size. -> Option A

5. Quick Check:

   Dynamic size needs slices = A [OK]

Hint: Slices provide dynamic size, arrays do not [OK]

Common Mistakes:

• Trying to resize arrays manually
• Using large fixed arrays to simulate flexibility
• Confusing maps with dynamic arrays