For-in loop with ranges in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print numbers from 1 to 5.

Swift

for number in [1] {
    print(number)
}

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

A1 to 5

B1..5

C1...5

Drange(1,5)

Attempts:

3 left

💡 Hint

Common Mistakes

Using two dots instead of three dots for range.

Using Python-style range syntax.

The correct syntax for a closed range in Swift is 1...5, which includes both 1 and 5.

2fill in blank

medium

Complete the code to print numbers from 1 up to but not including 5.

Swift

for number in [1] {
    print(number)
}

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

A1..<5

Brange(1,5)

C1..5

D1...5

Attempts:

3 left

💡 Hint

Common Mistakes

Using closed range ... which includes the end value.

Using invalid range syntax.

The half-open range operator ..< includes the start but excludes the end, so 1..<5 prints 1, 2, 3, 4.

3fill in blank

hard

Fix the error in the code to print numbers from 1 to 3.

Swift

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

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

A1<3

B1...3

C1..3

Drange(1,3)

Attempts:

3 left

💡 Hint

Common Mistakes

Using two dots instead of three dots.

Using Python range syntax.

The correct closed range operator in Swift is ..., so 1...3 includes 1, 2, and 3.

4fill in blank

hard

Fill both blanks to create a loop that prints even numbers from 2 to 10.

Swift

for number in [1] {
    if number [2] 2 == 0 {
        print(number)
    }
}

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

A2...10

B%

C==

D2..<10

Attempts:

3 left

💡 Hint

Common Mistakes

Using half-open range which excludes 10.

Using equality operator instead of modulo.

The range 2...10 includes numbers 2 through 10. The modulo operator % checks if the number is divisible by 2 (even).

5fill in blank

hard

Fill all three blanks to create a dictionary of numbers and their squares for numbers 1 to 5, but only include squares greater than 10.

Swift

var squares = [Int: Int]()
for number in [3] {
    if number * number > 10 {
        squares[[1]] = [2]
    }
}

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

Anumber

Bnumber * number

C1...5

Dnumber * 2

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong variable for keys or values.

Using half-open range excluding 5.

Using multiplication by 2 instead of square.

Declare var squares as an empty dictionary of type [Int: Int]. Loop over the closed range 1...5. For each number where number * number > 10, assign squares[number] = number * number.

Practice

1. What does the following Swift code print?
for i in 1...3 { print(i) }

easy

A. 1 2

B. 1 2 3

C. 0 1 2 3

D. 2 3 4

Solution

1. Step 1: Understand the range operator

   The range 1...3 is a closed range including 1, 2, and 3.

2. Step 2: Loop prints each number in the range

   The loop prints 1, then 2, then 3 on separate lines.

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   Closed range includes last number = 1 2 3 [OK]

Hint: Closed range includes last number, so count all numbers [OK]

Common Mistakes:

• Thinking the last number is excluded
• Starting from 0 instead of 1
• Confusing closed and half-open ranges

2. Which of the following is the correct syntax for a for-in loop iterating from 0 to 4 (excluding 4) in Swift?

easy

A. for i in 0...4 { }

B. for i in 0 to 4 { }

C. for i in 0..<4 { }

D. for i = 0; i < 4; i++ { }

Solution

1. Step 1: Identify the correct range syntax

   0..<4 is a half-open range including 0,1,2,3 but excluding 4.

2. Step 2: Check Swift for-in loop syntax

   Swift uses 'for variable in range { }' syntax; 'for i in 0..<4 { }' is correct.

3. Final Answer:

   for i in 0..<4 { } -> Option C

4. Quick Check:

   Half-open range excludes last number = for i in 0..<4 { } [OK]

Hint: Use '..<' for half-open range excluding last number [OK]

Common Mistakes:

• Using '...' when last number should be excluded
• Using 'to' keyword which is invalid in Swift
• Using C-style for loop syntax which is not valid in Swift

3. What is the output of this Swift code?

var sum = 0
for number in 1..<5 {
  sum += number
}
print(sum)

medium

A. 10

B. 15

C. 14

D. Error

Solution

1. Step 1: Identify the range and loop values

   The range 1..<5 includes 1, 2, 3, 4 (excluding 5).

2. Step 2: Calculate the sum of these numbers

   Sum = 1 + 2 + 3 + 4 = 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Sum of 1 to 4 = 10 [OK]

Hint: Half-open range excludes last number; sum 1+2+3+4 = 10 [OK]

Common Mistakes:

• Including 5 in the sum
• Adding numbers incorrectly
• Confusing closed and half-open ranges

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

for i in 1..< { print(i) }

medium

A. No error, code runs fine

B. Using wrong loop variable

C. Using closed range instead of half-open

D. Missing end value in range

Solution

1. Step 1: Check the range syntax

   The range 1..< is incomplete; it misses the end value after '..<' operator.

2. Step 2: Identify the error type

   This causes a syntax error because Swift expects a number after '..<' to define the range.

3. Final Answer:

   Missing end value in range -> Option D

4. Quick Check:

   Range must have start and end values [OK]

Hint: Range must have start and end values, '..<' alone is invalid [OK]

Common Mistakes:

• Leaving out the end value in range
• Confusing '..<' with '...' syntax
• Assuming loop variable causes error

5. You want to print all even numbers from 2 to 10 inclusive using a for-in loop with a range. Which code correctly does this?

hard

A. for i in 2...10 where i % 2 == 0 { print(i) }

B. for i in 2..<10 { if i % 2 == 0 { print(i) } }

C. for i in 2...10 { if i % 2 == 1 { print(i) } }

D. for i in 2...9 where i % 2 == 0 { print(i) }

Solution

1. Step 1: Understand the range and condition

   We want even numbers from 2 to 10 inclusive, so use closed range 2...10.

2. Step 2: Use 'where' clause to filter even numbers

   The 'where i % 2 == 0' filters only even numbers in the loop.

3. Final Answer:

   for i in 2...10 where i % 2 == 0 { print(i) } -> Option A

4. Quick Check:

   Closed range + where filter = for i in 2...10 where i % 2 == 0 { print(i) } [OK]

Hint: Use closed range and 'where' to filter even numbers [OK]

Common Mistakes:

• Using half-open range excluding 10
• Printing odd numbers by mistake
• Forgetting to filter even numbers