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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to loop through all elements in the array and print each one.

Swift

let fruits = ["Apple", "Banana", "Cherry"]
for [1] in fruits {
    print([1])
}

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

Aindex

Bfruit

Citem

Dfruits

Attempts:

3 left

💡 Hint

Common Mistakes

Using the collection name instead of a variable for each element.

Using a variable name that suggests an index instead of an element.

In a for-in loop, the variable (here fruit) represents each element in the collection.

2fill in blank

medium

Complete the code to loop through the dictionary and print each key and value.

Swift

let ages = ["Alice": 25, "Bob": 30, "Charlie": 35]
for ([1], age) in ages {
    print("\([1]) is \(age) years old")
}

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

Akey

Bage

Cname

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using the value variable name for the key.

Using a variable name that does not represent keys.

When looping through a dictionary, the first variable is the key (here key), and the second is the value.

3fill in blank

hard

Fix the error in the code to correctly loop through the set and print each element.

Swift

let colors: Set = ["Red", "Green", "Blue"]
for [1] in colors {
    print([1])
}

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

Aindex

Bcolors

Ccolor

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using the collection name instead of a single element variable.

Using a variable name that implies an index which sets do not have.

The loop variable should represent each element in the set, so 'color' is correct.

4fill in blank

hard

Fill both blanks to create a dictionary that maps each word to its length if the length is greater than 3 using reduce.

Swift

let words = ["cat", "house", "dog", "elephant"]
let lengths = words.reduce(into: [String: Int]()) { result, [1] in
    if [2] > 3 {
        result[[1]] = [2]
    }
}

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

Aword

Bword.count

Cword.length

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'word.length' which is not valid in Swift.

Using 'count' alone without specifying the variable.

In Swift, to create a dictionary from a collection, use the element as the key and its count as the value.

5fill in blank

hard

Fill all three blanks to create a for-in loop that prints each index and element from the array.

Swift

let animals = ["dog", "cat", "bird"]
for ([1], [2]) in animals.[3]() {
    print("Index \([1]): \([2])")
}

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

Aindex

Belement

Cenumerated

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'items()' which is not a valid method.

Swapping index and element variable names.

Use 'enumerated()' to get index and element pairs from an array in Swift.

Practice

1. What does the following Swift code do?

let numbers = [1, 2, 3]
for number in numbers {
    print(number)
}

easy

A. Prints each number in the array one by one

B. Prints the entire array once

C. Causes a syntax error

D. Prints the sum of the numbers

Solution

1. Step 1: Understand the for-in loop structure

   The loop goes through each element in the array named 'numbers'.

2. Step 2: Observe the print statement inside the loop

   Each element is printed on its own line as the loop runs.

3. Final Answer:

   Prints each number in the array one by one -> Option A

4. Quick Check:

   for number in numbers prints each number [OK]

Hint: For-in loops print items one at a time [OK]

Common Mistakes:

• Thinking it prints the whole array at once
• Confusing the loop variable with the collection
• Expecting a sum instead of individual prints

2. Which of the following is the correct syntax for a for-in loop iterating over an array named fruits in Swift?

easy

A. for fruit in fruits { print(fruit) }

B. for (fruit : fruits) { print(fruit) }

C. for fruit to fruits { print(fruit) }

D. foreach fruit in fruits { print(fruit) }

Solution

1. Step 1: Recall Swift for-in loop syntax

   The correct syntax uses 'for variable in collection { }'.

2. Step 2: Compare options to syntax

   Only for fruit in fruits { print(fruit) } matches this syntax exactly.

3. Final Answer:

   for fruit in fruits { print(fruit) } -> Option A

4. Quick Check:

   Correct for-in syntax uses 'in' keyword [OK]

Hint: Remember: for item in collection { } is correct [OK]

Common Mistakes:

• Using 'to' instead of 'in'
• Using parentheses incorrectly
• Using 'foreach' which is not Swift syntax

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

let names = ["Anna", "Bob", "Cara"]
for name in names {
    print(name.count)
}

medium

A. 3 3 4

B. 3 4 3

C. 4 3 3

D. 4 3 4

Solution

1. Step 1: Identify the array elements and their lengths

   "Anna" has 4 letters, "Bob" has 3, "Cara" has 4.

2. Step 2: Understand the loop prints each name's character count

   The loop prints 4, then 3, then 4 on separate lines.

3. Final Answer:

   4 3 4 -> Option D

4. Quick Check:

   name.count matches each string length [OK]

Hint: Count letters of each name inside the loop [OK]

Common Mistakes:

• Mixing up the order of counts
• Counting letters incorrectly
• Assuming print outputs on same line

4. Find the error in this Swift code snippet:

let colors = ["red", "green", "blue"]
for color in colors
    print(color)
}

medium

A. Array declaration syntax is wrong

B. Variable name 'color' is invalid

C. Missing opening brace '{' after for loop

D. print statement should be outside the loop

Solution

1. Step 1: Check for proper loop syntax

   The for-in loop requires braces '{' and '}' to enclose the loop body.

2. Step 2: Identify missing opening brace

   The code has a closing brace '}' but no opening brace '{' after the for line.

3. Final Answer:

   Missing opening brace '{' after for loop -> Option C

4. Quick Check:

   for loops need braces around their body [OK]

Hint: Always use { } to wrap for loop code block [OK]

Common Mistakes:

• Forgetting opening brace
• Misplacing braces
• Assuming print can be outside without braces

5. You have a dictionary of student names and their scores:

let scores = ["Alice": 85, "Bob": 92, "Cara": 78]

Using a for-in loop, how do you print only the names of students who scored above 80?

hard

A. for name in scores.keys {
if scores[name] > 80 {
print(name)
}
}

B. for (name, score) in scores {
if score > 80 {
print(name)
}
}

C. for score in scores.values {
if score > 80 {
print(score)
}
}

D. for name in scores {
if scores[name] > 80 {
print(name)
}
}

Solution

1. Step 1: Understand dictionary iteration with key-value pairs

   Using 'for (name, score) in scores' lets you access both keys and values directly.

2. Step 2: Apply condition to print names with score above 80

   Inside the loop, check if score > 80, then print the name.

3. Final Answer:

   for (name, score) in scores { if score > 80 { print(name) } } -> Option B

4. Quick Check:

   Use (key, value) pairs to filter dictionary [OK]

Hint: Use (key, value) in dictionary to access both [OK]

Common Mistakes:

• Trying to loop only keys or values without pairing
• Forgetting to unwrap optional values
• Printing scores instead of names