Repeat-while loop in Swift - Mini Project: Build & Apply

Repeat-while Loop in Swift

📖 Scenario: You are creating a simple program that counts up from 1 until it reaches a certain number. This is like counting steps while walking until you reach your destination.

🎯 Goal: Build a Swift program that uses a repeat-while loop to count from 1 up to a given limit and then prints the final count.

📋 What You'll Learn

Create a variable called count starting at 1

Create a constant called limit with the value 5

Use a repeat-while loop to increase count by 1 until it is greater than limit

Print the final value of count

💡 Why This Matters

🌍 Real World

Counting steps or attempts until a goal is reached is common in games, apps, and devices.

💼 Career

Understanding loops like repeat-while helps in automating repeated tasks and controlling program flow in software development.

1

Create the initial count variable

Create a variable called count and set it to 1.

Swift

# Create a variable called count and set it to 1
# Your code here

Hint

Use var to create a variable and assign it the value 1.

2

Set the limit constant

Create a constant called limit and set it to 5.

Swift

var count = 1
# Create a constant called limit and set it to 5
# Your code here

Hint

Use let to create a constant and assign it the value 5.

3

Use a repeat-while loop to count up

Write a repeat-while loop that increases count by 1 each time, and continues while count is less than or equal to limit.

Swift

var count = 1
let limit = 5
# Write a repeat-while loop to increase count by 1 while count is less than or equal to limit
# Your code here

Hint

Use repeat { ... } while condition syntax. Inside the loop, add 1 to count.

4

Print the final count

Write a print statement to display the value of count.

Swift

var count = 1
let limit = 5
repeat {
    count += 1
} while count <= limit
# Print the value of count
# Your code here

Hint

Use print(count) to show the final number.

Practice

1. What is the main difference between a repeat-while loop and a while loop in Swift?

easy

A. A repeat-while loop runs only once and never repeats.

B. A repeat-while loop checks the condition before running the code block.

C. A repeat-while loop cannot be used with Boolean conditions.

D. A repeat-while loop runs the code block at least once before checking the condition.

Solution

1. Step 1: Understand loop behavior

   A while loop checks the condition before running the code block, so it may not run at all if the condition is false initially.

2. Step 2: Compare with repeat-while

   A repeat-while loop runs the code block first, then checks the condition to decide if it should repeat, guaranteeing at least one execution.

3. Final Answer:

   A repeat-while loop runs the code block at least once before checking the condition. -> Option D

4. Quick Check:

   Repeat-while runs first, then checks condition [OK]

Hint: Repeat-while always runs code once before checking condition [OK]

Common Mistakes:

• Thinking repeat-while checks condition first
• Confusing repeat-while with while loop
• Believing repeat-while can't repeat

2. Which of the following is the correct syntax for a repeat-while loop in Swift?

easy

A. repeat (condition) { /* code */ }

B. repeat { /* code */ } while condition

C. while condition { /* code */ } repeat

D. do { /* code */ } while condition

Solution

1. Step 1: Recall Swift syntax for repeat-while

   The correct syntax starts with the keyword repeat, followed by a code block in braces, then the while keyword with the condition.

2. Step 2: Check each option

   repeat { /* code */ } while condition matches the correct syntax exactly. repeat (condition) { /* code */ } incorrectly places the condition in parentheses after repeat. while condition { /* code */ } repeat mixes while and repeat incorrectly. do { /* code */ } while condition uses do-while which is not valid Swift syntax.

3. Final Answer:

   repeat { /* code */ } while condition -> Option B

4. Quick Check:

   repeat { } while condition syntax [OK]

Hint: Remember: repeat { } while condition is the correct form [OK]

Common Mistakes:

• Using do-while instead of repeat-while
• Placing condition inside parentheses after repeat
• Mixing while and repeat keywords

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

var count = 3
repeat {
    print(count)
    count -= 1
} while count > 0

medium

A. 3 2 1

B. 2 1 0

C. 3 2 1 0

D. 1 2 3

Solution

1. Step 1: Trace the loop iterations

   Initial count is 3. The loop prints count, then decreases it by 1. It repeats while count > 0.

2. Step 2: List printed values

   First iteration: print 3, count becomes 2.
   Second iteration: print 2, count becomes 1.
   Third iteration: print 1, count becomes 0.
   Loop stops because count is not > 0.

3. Final Answer:

   3 2 1 -> Option A

4. Quick Check:

   Prints 3,2,1 then stops [OK]

Hint: Count down prints before condition check, stops at zero [OK]

Common Mistakes:

• Including 0 in output
• Printing after decrement instead of before
• Confusing order of printed numbers

4. Identify the error in this Swift repeat-while loop code:

var x = 5
repeat {
    print(x)
    x += 1
} while x < 5

medium

A. No error; the loop runs exactly once.

B. The loop will never run because condition is false initially.

C. Syntax error: missing parentheses around condition.

D. The loop will run infinitely because x keeps increasing.

Solution

1. Step 1: Analyze loop condition and variable change

   Initial x is 5. The loop runs once before checking condition. Inside loop, x increases by 1 each time.

2. Step 2: Check condition after first iteration

   After first iteration, x becomes 6. Condition is x < 5, which is false, so loop should stop. But since x increases, if condition was true, it would never stop. Here, it stops after one iteration.

3. Step 3: Re-examine the condition logic

   Actually, since x starts at 5, condition x < 5 is false, so loop runs once then stops. No infinite loop.

4. Final Answer:

   No error; the loop runs exactly once. -> Option A

5. Quick Check:

   Loop runs once then stops [OK]

Hint: Check variable change and condition carefully to avoid infinite loops [OK]

Common Mistakes:

• Assuming infinite loop without checking condition
• Thinking condition needs parentheses
• Believing loop won't run at all

5. You want to use a repeat-while loop to ask a user for a password until they enter "swift123". Which code snippet correctly implements this?

hard

A. repeat {
print("Enter password:")
input = readLine() ?? ""
} while input == "swift123"

B. var input = ""
while input != "swift123" {
print("Enter password:")
input = readLine() ?? ""
}

C. var input = ""
repeat {
print("Enter password:")
input = readLine() ?? ""
} while input != "swift123"

D. var input = ""
repeat {
input = readLine() ?? ""
} while input != "swift123"
print("Enter password:")

Solution

1. Step 1: Understand the requirement

   The loop must ask for password at least once and repeat until the user enters "swift123".

2. Step 2: Check each option

   var input = "" repeat { print("Enter password:") input = readLine() ?? "" } while input != "swift123" uses repeat-while, asks inside loop, and repeats while input is not "swift123". This matches the requirement.
   var input = "" while input != "swift123" { print("Enter password:") input = readLine() ?? "" } uses while loop, which may skip asking if input is already "swift123".
   repeat { print("Enter password:") input = readLine() ?? "" } while input == "swift123" repeats while input equals "swift123", which is opposite of requirement.
   var input = "" repeat { input = readLine() ?? "" } while input != "swift123" print("Enter password:") prints prompt after loop ends, so user is not prompted before input.

3. Final Answer:

   var input = "" repeat { print("Enter password:") input = readLine() ?? "" } while input != "swift123" -> Option C

4. Quick Check:

   Repeat-while asks first, repeats until correct [OK]

Hint: Use repeat-while to ask first, then check condition [OK]

Common Mistakes:

• Using while loop that may skip first prompt
• Reversing condition logic
• Prompting outside the loop