Range operators (... and ..<) in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of inclusive range loop

What is the output of this Swift code using the inclusive range operator ...?

Swift

for i in 1...3 {
    print(i, terminator: ",")
}

A 2,3,4,

B 1,2,

C 1,2,3,4,

D 1,2,3,

💡 Hint

Inclusive range includes both start and end values.

The ... operator creates a range that includes both the start and the end values. So the loop runs for 1, 2, and 3.

❓ Predict Output

intermediate

Output of half-open range loop

What is the output of this Swift code using the half-open range operator ..<?

Swift

for i in 1..<4 {
    print(i, terminator: "-")
}

A 1-2-3-

B 1-2-3-4-

C 2-3-4-

D 1-2-

💡 Hint

Half-open range excludes the end value.

The ..< operator creates a range that includes the start but excludes the end. So the loop runs for 1, 2, and 3.

🔧 Debug

advanced

Why does this range cause a runtime error?

Consider this Swift code snippet:

let numbers = [10, 20, 30]
for i in 0...numbers.count {
    print(numbers[i])
}

What error will this code cause when run?

A No error, prints all elements

B Index out of range runtime error

C Syntax error: missing colon

D Type error: cannot subscript array with Int

💡 Hint

Check the range bounds against the array indices.

The 0...numbers.count range includes the value 3, but the array indices go from 0 to 2. Accessing numbers[3] causes an index out of range error.

🧠 Conceptual

advanced

Count of elements in a half-open range

How many elements are in the range 5..<10 in Swift?

A 5

B 6

C 4

D 10

💡 Hint

Count is end minus start for half-open ranges.

The half-open range 5..<10 includes 5,6,7,8,9 which is 5 elements.

🚀 Application

expert

Using range operators to slice arrays

Given let arr = ["a", "b", "c", "d", "e"], which option correctly extracts the subarray ["b", "c", "d"] using range operators?

A arr[0..<3]

B arr[1...3]

C arr[1..<4]

D arr[2...4]

💡 Hint

Remember that array indices start at 0 and half-open ranges exclude the upper bound.

The subarray ["b", "c", "d"] corresponds to indices 1, 2, and 3. The half-open range 1..<4 includes 1, 2, and 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