Swift REPL and Playgrounds - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Hello, Swift!" in a Playground.

Swift

print([1])

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

A'Hello, Swift!'

B"Hello, Swift!"

CHello, Swift!

DHello Swift

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use quotes around the string.

Using single quotes instead of double quotes.

In Swift, strings must be enclosed in double quotes to be printed correctly.

2fill in blank

medium

Complete the code to declare a variable named 'count' with value 10 in Swift REPL.

Swift

var count = [1]

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

A"10"

Bcount

Cten

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Putting numbers inside quotes, which makes them strings.

Using variable names instead of values.

Variables holding numbers should be assigned numeric values without quotes.

3fill in blank

hard

Fix the error in the code to add two numbers and print the result.

Swift

let sum = 5 [1] 3
print(sum)

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

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Using invalid operators.

The plus sign (+) adds two numbers in Swift.

4fill in blank

hard

Fill both blanks in the loop to build a dictionary that maps words to their lengths for words longer than 3 characters. (Assume `let words = ["hello", "hi", "world", "a"]` is defined.)

Swift

var lengths: [String: Int] = [:]
for word in words {
  if word.count > 3 {
    lengths[[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 (use .count).

Using 'count' alone without specifying the word.

In Swift, use a for loop to build the dictionary, with 'word' as key and 'word.count' as value.

5fill in blank

hard

Fill all three blanks in the loop to create a dictionary from a list of tuples where keys are uppercase and values are doubled. (Assume `let data: [(String, Int)] = [("apple", 5), ("banana", 3)]` is defined.)

Swift

var transformed: [String: Int] = [:]
for ([3], [2]) in data {
  transformed[[1].uppercased()] = [2] * 2
}

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

Akey

Bvalue

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names that don't match between the tuple and usage.

Not uppercasing the key or doubling the value.

Using 'val' instead of 'value'.

Use 'key' for the first and third blanks to access the tuple key, and 'value' for the second blank to double the value. Note the tuple destructuring in the for loop.

Practice

1. What is the main purpose of Swift Playgrounds?

easy

A. To provide an interactive environment to write and test Swift code easily

B. To compile Swift code into an executable file

C. To manage Swift project dependencies

D. To deploy Swift apps to the App Store

Solution

1. Step 1: Understand what Playgrounds offer

   Swift Playgrounds allow users to write and run Swift code interactively with immediate feedback.

2. Step 2: Compare options with Playgrounds' purpose

   Options B, C, and D describe other development tasks, not the main purpose of Playgrounds.

3. Final Answer:

   To provide an interactive environment to write and test Swift code easily -> Option A

4. Quick Check:

   Playgrounds = Interactive coding environment [OK]

Hint: Playgrounds = interactive coding + instant results [OK]

Common Mistakes:

• Confusing Playgrounds with full app deployment tools
• Thinking Playgrounds compile apps for release
• Mixing Playgrounds with dependency managers

2. Which of the following is the correct way to start the Swift REPL in a terminal?

easy

A. swift run

B. swift

C. swift repl

D. swift playground

Solution

1. Step 1: Recall the command to start Swift REPL

   Typing swift alone in the terminal starts the Swift REPL environment.

2. Step 2: Check other options

   swift run runs a Swift package, swift repl is not a valid command, and swift playground does not start REPL.

3. Final Answer:

   swift -> Option B

4. Quick Check:

   Start REPL with 'swift' command [OK]

Hint: Just type 'swift' to open REPL in terminal [OK]

Common Mistakes:

• Using 'swift run' which runs packages, not REPL
• Typing 'swift repl' which is invalid
• Confusing REPL with Playgrounds commands

3. What will be the output when you run this code in Swift REPL?

let x = 5
let y = 10
x + y

medium

A. 15

B. x + y

C. SyntaxError

D. 10

Solution

1. Step 1: Evaluate the variables and expression

   Variables x and y are assigned 5 and 10 respectively. The expression x + y sums them.

2. Step 2: Calculate the sum

   5 + 10 equals 15, so the REPL outputs 15.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Add values step-by-step to find output [OK]

Common Mistakes:

• Expecting the expression to print the code itself
• Thinking REPL shows errors for valid expressions
• Confusing variable values

4. You wrote this code in a Swift Playground but it shows an error:

var greeting = "Hello"
greeting += 5

What is the problem?

medium

A. You must use '==' instead of '+='

B. Variable 'greeting' should be a constant

C. You cannot add an integer to a string directly

D. Strings cannot be modified in Playgrounds

Solution

1. Step 1: Analyze the code operation

   The code tries to add an integer (5) to a string variable using '+='.

2. Step 2: Understand Swift type rules

   Swift does not allow adding an Int directly to a String; types must match or be converted.

3. Final Answer:

   You cannot add an integer to a string directly -> Option C

4. Quick Check:

   String + Int without conversion causes error [OK]

Hint: Check data types before combining values [OK]

Common Mistakes:

• Thinking '+=' works with different types
• Assuming strings are immutable in Playgrounds
• Confusing assignment operators

5. You want to quickly test a function that calculates the square of a number using Swift Playgrounds. Which approach is best?

hard

A. Write the function in a text editor and run it later in the terminal

B. Write the function in a Swift file and compile it with Xcode without running

C. Use Swift REPL but avoid Playgrounds because it can't run functions

D. Write the function in Playgrounds and call it with test values to see results immediately

Solution

1. Step 1: Understand Playgrounds' interactive nature

   Playgrounds allow writing functions and immediately running them with test inputs to see results.

2. Step 2: Evaluate other options

   Write the function in a Swift file and compile it with Xcode without running compiles but does not run immediately; Use Swift REPL but avoid Playgrounds because it can't run functions is false because Playgrounds can run functions; Write the function in a text editor and run it later in the terminal delays testing.

3. Final Answer:

   Write the function in Playgrounds and call it with test values to see results immediately -> Option D

4. Quick Check:

   Playgrounds = quick function testing [OK]

Hint: Use Playgrounds for instant function testing [OK]

Common Mistakes:

• Thinking Playgrounds can't run functions
• Confusing compiling with running
• Delaying testing by using external editors