Why maps are used in Go - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a map that stores string keys and int values.

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 instead of map syntax.

Trying to declare a map without specifying key and value types.

Maps in Go are declared using the map[keyType]valueType syntax. Here, map[string]int means keys are strings and values are integers.

2fill in blank

medium

Complete the code to initialize a map using the make function.

Go

scores := [1](map[string]int)

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

Amake

Bcreate

Cnew

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using new instead of make for maps.

Trying to initialize maps without using make or a literal.

The make function is used to create and initialize maps in Go. It allocates memory for the map.

3fill in blank

hard

Fix the error in the code to correctly add a key-value pair to the map.

Go

m := make(map[string]int)
m[[1]] = 10

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

Am

Bage

C10

D"age"

Attempts:

3 left

💡 Hint

Common Mistakes

Using an integer or variable without quotes as a string key.

Using the map variable itself as a key.

Map keys must be of the declared key type. Since the key type is string, the key must be a string literal like "age".

4fill in blank

hard

Fill both blanks to create a map comprehension that stores word lengths for words longer than 3 characters.

Go

lengths := map[string]int{
	[1]: len([2]) for _, [2] := range words if len([2]) > 3
}

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

A"word"

Bword

Cwords

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using the slice words as a key.

Not quoting the key string.

In Go, map literals don't support comprehensions like Python. This task is a trick to think about keys and values: keys are strings (words), so use "word" as a key placeholder and word as the variable holding each word.

5fill in blank

hard

Fill all three blanks to check if a key exists in the map and print its value.

Go

if val, [1] := m[[2]]; [3] {
	fmt.Println(val)
}

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

Aok

B"key"

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Using the value variable instead of the boolean check.

Not quoting the key string.

In Go, to check if a key exists in a map, you use the two-value assignment: val, ok := m["key"]. Then you check if ok is true.

Practice

1. Why are maps used in Go programming?

easy

A. To create graphical user interfaces

B. To perform mathematical calculations

C. To store data with keys for fast lookup

D. To handle file input and output

Solution

1. Step 1: Understand the purpose of maps

   Maps store data in key-value pairs, allowing quick access to values using keys.

2. Step 2: Compare with other uses

   Maps are not used for calculations, GUI, or file handling, which are handled by other packages or types.

3. Final Answer:

   To store data with keys for fast lookup -> Option C

4. Quick Check:

   Maps = Fast key-based data access [OK]

Hint: Maps = key-value pairs for quick data access [OK]

Common Mistakes:

• Confusing maps with slices or arrays
• Thinking maps are for calculations
• Assuming maps handle files or UI

2. Which of the following is the correct way to create a map in Go?

easy

A. var m = map[string]int{1, 2, 3}

B. var m map[string]int = make(map[string]int)

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

D. var m = make([]string, 5)

Solution

1. Step 1: Identify correct map creation syntax

   Maps are created using make with the syntax: make(map[keyType]valueType).

2. Step 2: Check each option

   var m map[string]int = make(map[string]int) uses make with map[string]int correctly. Options B and D create slices, and A has wrong map literal syntax.

3. Final Answer:

   var m map[string]int = make(map[string]int) -> Option B

4. Quick Check:

   Use make(map[key]value) to create maps [OK]

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

Common Mistakes:

• Using slice syntax instead of map
• Forgetting to use make before adding items
• Incorrect map literal syntax

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. Compilation error

C. 0

D. 8

Solution

1. Step 1: Understand map assignments

   Keys "apple" and "banana" are assigned values 5 and 3 respectively in the map.

2. Step 2: Calculate the sum of values

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

3. Final Answer:

   8 -> Option D

4. Quick Check:

   5 + 3 = 8 [OK]

Hint: Sum values by keys to get output [OK]

Common Mistakes:

• Concatenating values as strings
• Expecting zero for missing keys
• Thinking code has syntax errors

4. What is wrong with this Go code snippet?

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

medium

A. Map is not initialized with make before use

B. Key type should be int, not string

C. Value type should be string, not int

D. fmt.Println cannot print map values

Solution

1. Step 1: Check map initialization

   The map m is declared but not initialized with make, so it is nil and cannot store values.

2. Step 2: Understand consequences

   Assigning to a nil map causes a runtime panic. The map must be created with make before adding items.

3. Final Answer:

   Map is not initialized with make before use -> Option A

4. Quick Check:

   Use make to initialize maps before adding keys [OK]

Hint: Always initialize maps with make before adding items [OK]

Common Mistakes:

• Forgetting to initialize map before use
• Confusing map declaration with initialization
• Assuming fmt.Println can't print map values

5. You want to count how many times each word appears in a list of words using a map in Go. Which approach is correct?

hard

A. Create a map[string]int with make, then loop words and increment counts

B. Use a slice of strings and append each word multiple times

C. Create a map[int]string and store counts as keys

D. Use a single string variable to store all words concatenated

Solution

1. Step 1: Choose correct data structure

   Counting word occurrences requires a map with words as keys and counts as values, so map[string]int is suitable.

2. Step 2: Implement counting logic

   Initialize the map with make, then loop through the list, incrementing the count for each word key.

3. Final Answer:

   Create a map[string]int with make, then loop words and increment counts -> Option A

4. Quick Check:

   Use map[string]int to count word frequencies [OK]

Hint: Use map[string]int and increment counts in loop [OK]

Common Mistakes:

• Using slices instead of maps for counting
• Mixing key and value types in map
• Storing counts as keys instead of values