Range operators (... and ..<) in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a closed range from 1 to 5.

Swift

let range = 1 [1] 5
print(Array(range))

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

A..<

B...

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using ..< excludes the last number.

Using - or + is not valid for ranges.

The ... operator creates a closed range including both start and end values.

2fill in blank

medium

Complete the code to create a half-open range from 1 up to but not including 5.

Swift

let range = 1 [1] 5
print(Array(range))

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

A..<

B...

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using ... includes the last number.

Using + or - is not valid for ranges.

The ..< operator creates a half-open range that excludes the upper bound.

3fill in blank

hard

Fix the error in the code to print numbers from 1 to 4 using a half-open range.

Swift

for i in 1 [1] 5 {
    print(i)
}

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

A...

B+

C..<

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using ... includes 5, which is not desired here.

Using + or - is invalid syntax.

Using ..< creates a range from 1 up to but not including 5, so it prints 1 to 4.

4fill in blank

hard

Fill both blanks to create a dictionary with word lengths for words longer than 3 characters.

Swift

let words = ["apple", "bat", "carrot", "dog"]
let lengths = Dictionary(uniqueKeysWithValues: words.filter { word in [2] }.map { word in (word, [1]) } )

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

Aword.count

Bword.count > 3

Cword.count < 3

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using word instead of word.count for length.

Filtering words with length less than 3.

We use word.count to get the length and filter words with length greater than 3.

5fill in blank

hard

Fill all three blanks to create a dictionary of uppercase words and their lengths for words longer than 3 characters.

Swift

let words = ["apple", "bat", "carrot", "dog"]
let lengths = Dictionary(uniqueKeysWithValues: words.filter { word in [3] }.map { word in ([1], [2]) } )

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

Aword.uppercased()

Bword.count

Cword.count > 3

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using word instead of word.uppercased() for keys.

Not filtering words by length.

The keys are uppercase words, values are their lengths, filtered by length greater than 3.

Practice

1. What does the Swift range operator 1...5 represent?

easy

A. A range including numbers 1, 2, 3, 4, and 5

B. A range including numbers 1, 2, 3, and 4 only

C. A range excluding number 1 but including 5

D. A range excluding both 1 and 5

Solution

1. Step 1: Understand the closed range operator

   The ... operator creates a range that includes both the start and end values.

2. Step 2: Apply to the given range

   For 1...5, it includes 1, 2, 3, 4, and 5.

3. Final Answer:

   A range including numbers 1, 2, 3, 4, and 5 -> Option A

4. Quick Check:

   1...5 includes 5 [OK]

Hint: Remember: ... includes end number, ..< excludes it [OK]

Common Mistakes:

• Thinking ... excludes the last number
• Confusing ... with ..<
• Assuming ..< includes the end number

2. Which of the following is the correct syntax to create a half-open range from 0 to 9 in Swift?

easy

A. 0...9

B. 0..<10

C. 0..9

D. 0...10

Solution

1. Step 1: Identify half-open range syntax

   The half-open range operator in Swift is ..<, which includes the start but excludes the end.

2. Step 2: Apply to the range 0 to 9

   To include numbers 0 through 9, use 0..<10 because 10 is excluded.

3. Final Answer:

   0..<10 -> Option B

4. Quick Check:

   ..< excludes end [OK]

Hint: Use ..< to exclude the last number in range [OK]

Common Mistakes:

• Using ... when half-open range is needed
• Writing 0..9 which is invalid syntax
• Confusing end number inclusion

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

for i in 3..<6 {
    print(i, terminator: ",")
}

medium

A. 3,4,5,6,

B. 4,5,6,

C. 3,4,5,

D. 3,4,5,6

Solution

1. Step 1: Understand the range used in the loop

   The range 3..<6 includes 3, 4, and 5 but excludes 6.

2. Step 2: Trace the loop output

   The loop prints 3, then 4, then 5, each followed by a comma.

3. Final Answer:

   3,4,5, -> Option C

4. Quick Check:

   ..<6 excludes 6 [OK]

Hint: ..< excludes end; loop stops before 6 [OK]

Common Mistakes:

• Including 6 in output
• Missing commas in output
• Confusing terminator usage

4. The following Swift code has an error. What is the problem?

let range = 1..5
for num in range {
    print(num)
}

medium

A. The range operator .. is invalid in Swift

B. The loop variable num is not declared

C. The print statement syntax is incorrect

D. The range should start from 0

Solution

1. Step 1: Check the range operator used

   The code uses 1..5, which is not a valid range operator in Swift.

2. Step 2: Identify correct range operators

   Swift uses ... for closed ranges and ..< for half-open ranges, but not ...

3. Final Answer:

   The range operator .. is invalid in Swift -> Option A

4. Quick Check:

   Invalid operator .. causes error [OK]

Hint: Use ... or ..<, never .. alone [OK]

Common Mistakes:

• Using .. instead of ... or ..<
• Assuming .. is a valid operator
• Ignoring compiler error messages

5. You want to create a Swift array containing numbers from 5 to 15, excluding 15, and then print only the even numbers. Which code snippet correctly uses range operators and filtering?

hard

A. let numbers = Array(5...15).filter { $0 % 2 == 0 }
print(numbers)

B. let numbers = Array(5..15).filter { $0 % 2 == 0 }
print(numbers)

C. let numbers = Array(5..<14).filter { $0 % 2 == 0 }
print(numbers)

D. let numbers = Array(5..<15).filter { $0 % 2 == 0 }
print(numbers)

Solution

1. Step 1: Choose correct range excluding 15

   To exclude 15, use the half-open range 5..<15, which includes 5 up to 14.

2. Step 2: Filter even numbers

   The filter condition { $0 % 2 == 0 } selects even numbers from the array.

3. Step 3: Verify other options

   let numbers = Array(5...15).filter { $0 % 2 == 0 } print(numbers) includes 15, let numbers = Array(5..15).filter { $0 % 2 == 0 } print(numbers) uses invalid operator .., and let numbers = Array(5..<14).filter { $0 % 2 == 0 } print(numbers) uses 5..<14 which goes only up to 13, missing the even number 14.

4. Final Answer:

   let numbers = Array(5..<15).filter { $0 % 2 == 0 } print(numbers) -> Option D

5. Quick Check:

   ..< excludes end, filter selects even [OK]

Hint: Use ..< to exclude end, then filter even numbers [OK]

Common Mistakes:

• Using ... to include 15 mistakenly
• Using invalid .. operator
• Not filtering correctly for even numbers