Map use cases in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Go

var scores map[string][1]

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

Afloat64

Bstring

Cint

Dbool

Attempts:

3 left

💡 Hint

Common Mistakes

Using string as the value type instead of int.

Confusing key and value types.

The map stores string keys and integer values, so the value type is int.

2fill in blank

medium

Complete the code to initialize the map before adding elements.

Go

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

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

Afloat64

Bstring

Cbool

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using string or other types instead of int.

Forgetting to initialize the map before use.

The map values are integers, so make must specify int as the value type.

3fill in blank

hard

Fix the error in the code that adds a new key-value pair to the map.

Go

scores[[1]] = 90

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

A"Alice"

BAlice

C90

Dscore

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted string keys.

Using a number or variable name instead of a string literal.

Map keys of type string must be enclosed in double quotes when used as literals.

4fill in blank

hard

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

Go

value, [1] := scores["Bob"]
if [2] {
    fmt.Println("Bob's score:", value)
}

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

Aok

Bexists

Ctrue

Dfound

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in assignment and condition.

Using a string or non-boolean variable in the if condition.

The idiomatic way in Go to check if a key exists is to use the second value, often named ok, which is a boolean.

5fill in blank

hard

Fill all three blanks to declare the words slice, initialize the lengths map, and populate it with lengths for words longer than 3 characters.

Go

[1] := []string{"go", "code", "map", "function"}
[2] := make(map[string][3])
for _, w := range [1] {
    if len(w) > 3 {
        [2][w] = len(w)
    }
}

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

Awords

Blengths

Cint

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping slice and map variable names.

Using string instead of int for map values.

BLANK_1 declares the words slice, BLANK_2 the lengths map variable, and BLANK_3 the int value type for storing lengths.

Practice

1. What is the primary use of a map in Go?

easy

A. To store data with keys for fast lookup

B. To perform mathematical calculations

C. To create user interfaces

D. To handle file input/output

Solution

1. Step 1: Understand the purpose of a map

   A map in Go is a collection of key-value pairs, designed for fast data retrieval using keys.

2. Step 2: Compare with other options

   Options B, C, and D describe unrelated tasks like calculations, UI, or file handling, which are not the main use of maps.

3. Final Answer:

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

4. Quick Check:

   Maps = key-value storage [OK]

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

Common Mistakes:

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

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

easy

A. m := make([]string, 0)

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

C. m := map[string]int

D. m := []int{}

Solution

1. Step 1: Identify map creation syntax

   In Go, maps are created using make(map[keyType]valueType). var m map[string]int = make(map[string]int) uses this correctly.

2. Step 2: Check other options

   m := []int{} creates a slice, not a map. m := map[string]int is invalid syntax for map creation. m := make([]string, 0) creates a slice, not a map.

3. Final Answer:

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

4. Quick Check:

   Use make() to create maps [OK]

Hint: Use make() to create maps before use [OK]

Common Mistakes:

• Using slice syntax instead of map syntax
• Not using make() to initialize maps
• Confusing map and slice creation

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

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

medium

A. 8

B. 53

C. 0

D. Compilation error

Solution

1. Step 1: Understand map assignments

   The map m stores integers with string keys. "apple" maps to 5, "banana" maps to 3.

2. Step 2: Calculate the sum

   Adding m["apple"] + m["banana"] equals 5 + 3 = 8.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   5 + 3 = 8 [OK]

Hint: Sum values by accessing keys directly [OK]

Common Mistakes:

• Concatenating values as strings
• Expecting zero for existing keys
• Thinking code causes error

4. What is wrong with this Go code snippet?

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

medium

A. Cannot assign int values to map

B. Key "key" is invalid syntax

C. Map is not initialized with make() before use

D. fmt.Println cannot print map values

Solution

1. Step 1: Check map initialization

   The map m is declared but not initialized with make(). This causes a runtime panic on assignment.

2. Step 2: Understand consequences

   Without initialization, m["key"] = 10 causes a panic: assignment to nil map.

3. Final Answer:

   Map is not initialized with make() before use -> Option C

4. Quick Check:

   Initialize maps with make() [OK]

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

Common Mistakes:

• Forgetting to initialize map before use
• Assuming declaration is enough
• Misunderstanding map assignment rules

5. Given a map m := map[string]int{"a": 1, "b": 0, "c": 3}, which code snippet correctly checks if key "b" exists and its value is non-zero?

hard

A. if _, ok := m["b"]; ok { fmt.Println("Exists and non-zero") }

B. if m["b"] == 0 { fmt.Println("Exists and non-zero") }

C. if m["b"] >= 0 { fmt.Println("Exists and non-zero") }

D. if val, ok := m["b"]; ok && val != 0 { fmt.Println("Exists and non-zero") }

Solution

1. Step 1: Understand map key existence check

   Using val, ok := m["b"] lets us check if key "b" exists (ok) and get its value (val).

2. Step 2: Check value is non-zero

   The condition ok && val != 0 ensures key exists and value is not zero.

3. Final Answer:

   if val, ok := m["b"]; ok && val != 0 { fmt.Println("Exists and non-zero") } -> Option D

4. Quick Check:

   Check key existence and value together [OK]

Hint: Use val, ok := map[key] to check existence and value [OK]

Common Mistakes:

• Checking value without verifying key existence
• Assuming zero means key missing
• Using only ok without value check