Map creation in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a map from string to int.

Go

var ages [1]

Drag options to blanks, or click blank then click option'

A[]int

Bmap[string]int

Cstruct{}

Dchan int

Attempts:

3 left

💡 Hint

Common Mistakes

Using slice syntax []int instead of map syntax.

Confusing map with channel or struct types.

The correct syntax to declare a map from string to int in Go is map[string]int.

2fill in blank

medium

Complete the code to initialize an empty map of string to int.

Go

ages := [1]

Drag options to blanks, or click blank then click option'

Amake(map[string]int)

Bnew(map[string]int)

Cmake([]int, 0)

D[]string{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using make with slice type instead of map type.

Using new which returns a pointer, not a map.

To create an empty map in Go, use make(map[string]int).

3fill in blank

hard

Fix the error in the map initialization code.

Go

var ages = [1]

Drag options to blanks, or click blank then click option'

Amap[string]int

Bmap[string]int()

Cmap[string]int{}

Dmap[string]int[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of curly braces for map literals.

Using square brackets which are for slices or arrays.

To initialize a map with a literal, use map[string]int{}. Parentheses or brackets are incorrect here.

4fill in blank

hard

Fill both blanks to create a map with initial values.

Go

scores := [1]{
	"Alice": [2],
	"Bob": 90,
}

Drag options to blanks, or click blank then click option'

Amap[string]int

B85

C80

D[]int

Attempts:

3 left

💡 Hint

Common Mistakes

Using slice type instead of map type.

Using a string instead of an integer for the value.

The map type is map[string]int and the value for "Alice" is 85.

5fill in blank

hard

Fill all three blanks to create a map and add a new key-value pair.

Go

items := [1]{
	"pen": 5,
	"notebook": 10,
}
items[[2]] = [3]

Drag options to blanks, or click blank then click option'

Amap[string]int

B"eraser"

C3

D[]string

Attempts:

3 left

💡 Hint

Common Mistakes

Using slice type instead of map type.

Forgetting quotes around string keys.

Assigning a string value instead of an integer.

The map type is map[string]int. The new key is "eraser" and the value is 3.

Practice

1. What is the correct way to create an empty map with string keys and int values in Go?

easy

A. m := make(map[string]int)

B. m := map[string]int()

C. m := new(map[string]int)

D. m := []string{}

Solution

1. Step 1: Understand map creation syntax

   In Go, the built-in function make is used to create maps with specified key and value types.

2. Step 2: Identify the correct syntax for an empty map

   make(map[string]int) creates an empty map with string keys and int values.

3. Final Answer:

   m := make(map[string]int) -> Option A

4. Quick Check:

   Use make(map[keyType]valueType) to create maps [OK]

Hint: Use make() with map[keyType]valueType to create maps [OK]

Common Mistakes:

• Using new() instead of make() for maps
• Trying to create map with slice syntax
• Confusing map literal with empty slice

2. Which of the following is a syntax error when creating a map in Go?

easy

A. m := make(map[int]string)

B. m := make(map[float64]int)

C. m := make(map[[]int]string)

D. m := map[int]string{}

Solution

1. Step 1: Check key type validity

   Map keys must be comparable types. Slices ([]int) are not comparable in Go.

2. Step 2: Identify invalid map key type

   Using []int as a key type causes a syntax error because slices cannot be map keys.

3. Final Answer:

   m := make(map[[]int]string) -> Option C

4. Quick Check:

   Map keys must be comparable types [OK]

Hint: Map keys cannot be slices or maps, only comparable types [OK]

Common Mistakes:

• Using slices or maps as map keys
• Confusing map literal with slice literal
• Ignoring key type restrictions

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

m := make(map[string]int)
m["apple"] = 5
m["banana"] = 3
fmt.Println(m["apple"] + m["banana"])

medium

A. 53

B. 8

C. 0

D. Compilation error

Solution

1. Step 1: Understand map assignments

   The map m stores key-value pairs: "apple"=5 and "banana"=3.

2. Step 2: Calculate the sum of values

   Adding m["apple"] (5) and m["banana"] (3) results in 8.

3. Final Answer:

   8 -> Option B

4. Quick Check:

   5 + 3 = 8 [OK]

Hint: Sum map values by accessing keys directly [OK]

Common Mistakes:

• Concatenating values as strings instead of adding
• Expecting zero for existing keys
• Forgetting to initialize map before use

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

var m map[string]int
m["key"] = 10
fmt.Println(m["key"])

medium

A. No error, prints 10

B. Syntax error in map declaration

C. Key type must be int, not string

D. Map declared but not initialized, causes runtime panic

Solution

1. Step 1: Check map initialization

   The map m is declared but not initialized with make, so it is nil.

2. Step 2: Understand runtime behavior

   Assigning to a nil map causes a runtime panic (error) because the map is not ready to store values.

3. Final Answer:

   Map declared but not initialized, causes runtime panic -> Option D

4. Quick Check:

   Declare + make before use to avoid panic [OK]

Hint: Always initialize maps with make() before adding keys [OK]

Common Mistakes:

• Forgetting to initialize map before assignment
• Assuming declaration alone creates usable map
• Confusing map declaration with slice declaration

5. Given a slice of strings keys := []string{"a", "b", "c"} and a slice of ints values := []int{1, 2, 3}, which code snippet correctly creates a map from keys to values?

hard

A. m := make(map[string]int)
for i := range keys {
m[keys[i]] = values[i]
}

B. m := map[string]int{}
for i, v := range values {
m[v] = keys[i]
}

C. m := make(map[int]string)
for i := 0; i < len(keys); i++ {
m[i] = keys[i]
}

D. m := make(map[string]int)
for i := 0; i < len(values); i++ {
m[values[i]] = keys[i]
}

Solution

1. Step 1: Match keys and values correctly

   Keys are strings, values are ints. The map must have type map[string]int.

2. Step 2: Verify loop and assignment

   m := make(map[string]int) for i := range keys { m[keys[i]] = values[i] } loops over keys and assigns m[keys[i]] = values[i], correctly pairing keys to values.

3. Final Answer:

   m := make(map[string]int) for i := range keys { m[keys[i]] = values[i] } -> Option A

4. Quick Check:

   Loop keys, assign values to map[key] [OK]

Hint: Loop keys, assign values to map[key] for correct pairing [OK]

Common Mistakes:

• Swapping keys and values in map assignment
• Using wrong map key or value types
• Not initializing map before assignment