Array Declaration and Initialization in DSA Go - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Array Initialization with Default Values

What is the output of the following Go code snippet that declares and initializes an array?

DSA Go

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

A [0 0 0 0 0]

B [1 1 1 1 1]

C [5 5 5 5 5]

D [0 1 2 3 4]

💡 Hint

Arrays in Go are initialized with zero values for their type.

In Go, when you declare an array without explicit initialization, all elements are set to the zero value of the element type. For int, zero value is 0.

❓ Predict Output

intermediate

Output of Array Initialization with Partial Values

What is the output of this Go code that partially initializes an array?

DSA Go

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

A [1 2 0 0 0]

B [1 2 3 4 5]

C [1 2 0 0]

D [0 0 0 0 0]

💡 Hint

Uninitialized elements in an array get the zero value of the type.

The array is declared with 5 elements, but only first two are initialized. The rest default to 0.

❓ Predict Output

advanced

Output of Array Initialization Using Index Keys

What will be printed by this Go program that initializes an array using index keys?

DSA Go

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

A [10 0 0 20 0]

B [2 4 10 20 0]

C [0 10 0 20 0]

D [0 0 10 0 20]

💡 Hint

Index keys specify which positions get assigned values.

Only positions 2 and 4 are assigned values 10 and 20 respectively. Others remain zero.

🔧 Debug

advanced

Identify the Error in Array Declaration

What error will this Go code produce when compiled?

DSA Go

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

A syntax error: unexpected [4]int

B cannot use [4]int literal (type [4]int) as type [3]int in assignment

C index out of range error

D no error, compiles successfully

💡 Hint

Array sizes must match exactly in Go assignments.

The declared array size is 3, but the literal has size 4. This causes a type mismatch error.

🧠 Conceptual

expert

Array Size Inference in Go

Which of the following array declarations in Go correctly infers the array size from the number of elements provided?

A var arr = [4]int{1, 2, 3, 4, 5}

B var arr [4]int = [...]int{1, 2, 3, 4}

C arr := [...]int{1, 2, 3, 4}

D arr := [4]int{...}

💡 Hint

The ... syntax lets Go count elements automatically.

Using [...] tells Go to infer the array size from the number of elements in the literal. Option C uses this correctly.

Practice

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

easy

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

B. var arr [5]int

C. arr := [5]int

D. arr := []int{5}

Solution

1. Step 1: Understand array declaration syntax in Go

   Arrays in Go are declared with a fixed size inside square brackets, followed by the type, e.g., var arr [5]int.

2. Step 2: Analyze each option

   var arr [5]int correctly declares an array of 5 integers. arr := [5]int uses shorthand but lacks the array literal {}, causing a syntax error. var arr []int = make([]int, 5) declares a slice, not an array. arr := []int{5} declares a slice with one element 5, not an array of size 5.

3. Final Answer:

   var arr [5]int -> Option B

4. Quick Check:

   Array declaration = var arr [5]int [OK]

Hint: Arrays use fixed size in brackets, slices do not [OK]

Common Mistakes:

• Confusing slices with arrays
• Using shorthand without initialization
• Incorrect size placement

2. Which of the following is the correct syntax to initialize an array with values 1, 2, 3 in Go?

easy

A. arr := []int{1, 2, 3}

B. arr := [3]int(1, 2, 3)

C. var arr [3]int = {1, 2, 3}

D. var arr = [3]int{1, 2, 3}

Solution

1. Step 1: Review array initialization syntax

   In Go, arrays are initialized with curly braces and values inside, e.g., [3]int{1, 2, 3}.

2. Step 2: Check each option

   var arr = [3]int{1, 2, 3} uses correct syntax. arr := [3]int(1, 2, 3) uses parentheses which is invalid. var arr [3]int = {1, 2, 3} misses the type keyword before braces. arr := []int{1, 2, 3} declares a slice, not an array.

3. Final Answer:

   var arr = [3]int{1, 2, 3} -> Option D

4. Quick Check:

   Array init with braces = var arr = [3]int{1, 2, 3} [OK]

Hint: Use curly braces {} for array initialization [OK]

Common Mistakes:

• Using parentheses instead of braces
• Confusing slices with arrays
• Omitting type in declaration

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

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

medium

A. [10 20 0 0]

B. [10 20]

C. [0 0 0 0]

D. Compilation error

Solution

1. Step 1: Understand partial array initialization

   When an array is partially initialized, the remaining elements are set to zero values (0 for int).

2. Step 2: Analyze the given array

   The array size is 4, but only first two elements are initialized as 10 and 20. The last two elements default to 0.

3. Final Answer:

   [10 20 0 0] -> Option A

4. Quick Check:

   Partial init fills rest with zeros = [10 20 0 0] [OK]

Hint: Uninitialized array elements default to zero [OK]

Common Mistakes:

• Expecting only initialized elements in output
• Thinking partial init causes error
• Confusing slices with arrays

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

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

medium

A. No error, code is correct

B. Array size mismatch error

C. Syntax error in array declaration

D. Missing import statement

Solution

1. Step 1: Check array size and initialization

   The array is declared with size 3 but initialized with 2 values. Go allows this and fills the last element with zero.

2. Step 2: Verify syntax and imports

   No syntax error exists. Import is not mandatory if no external packages are used. The code compiles fine.

3. Final Answer:

   No error, code is correct -> Option A

4. Quick Check:

   Partial init allowed, no import needed [OK]

Hint: Partial initialization is allowed; missing imports only if used [OK]

Common Mistakes:

• Assuming size mismatch causes error
• Expecting import for main package
• Confusing slices with arrays

5. You want to declare an array of 5 integers in Go and initialize only the last element to 100, leaving others as zero. Which code snippet achieves this correctly?

hard

A. var arr = [5]int{0: 100}

B. var arr = [5]int{5: 100}

C. var arr = [5]int{4: 100}

D. var arr = [5]int{100}

Solution

1. Step 1: Understand indexed initialization in arrays

   Go allows initializing specific elements by index using syntax like {index: value}. Indexing starts at 0.

2. Step 2: Analyze each option

   var arr = [5]int{4: 100} initializes the element at index 4 (the last element in a 5-element array) to 100, others default to 0. var arr = [5]int{5: 100} uses index 5 which is out of range. var arr = [5]int{100} initializes only the first element. var arr = [5]int{0: 100} initializes index 0 to 100, not the last.

3. Final Answer:

   var arr = [5]int{4: 100} -> Option C

4. Quick Check:

   Use index 4 for last element in 5-size array [OK]

Hint: Index starts at 0; last element is index size-1 [OK]

Common Mistakes:

• Using out-of-range index
• Initializing first element instead of last
• Omitting index for specific element