While loop in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple while loop

What is the output of the following Swift code?

Swift

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

A

3
2
1

B

1
2
3

C

0
1
2
3

D

3
2
1
0

💡 Hint

Remember the loop runs while count is greater than zero and decreases count each time.

The loop starts with count = 3 and prints it, then decreases count by 1. It continues until count is no longer greater than 0, so it prints 3, 2, and 1.

❓ Predict Output

intermediate

While loop with break statement

What will be printed by this Swift code?

Swift

var i = 1
while i <= 5 {
    if i == 3 {
        break
    }
    print(i)
    i += 1
}

A

1
2

B

1
2
3

C

1
2
3
4
5

D

3
4
5

💡 Hint

The break statement stops the loop immediately when i equals 3.

The loop prints i starting from 1. When i becomes 3, the break stops the loop before printing 3, so only 1 and 2 are printed.

❓ Predict Output

advanced

While loop with continue statement

What is the output of this Swift code snippet?

Swift

var n = 0
while n < 5 {
    n += 1
    if n == 3 {
        continue
    }
    print(n)
}

A

1
2
3
4

B

1
2
3
4
5

C

2
3
4
5

D

1
2
4
5

💡 Hint

The continue skips printing when n equals 3.

The loop increments n first. When n is 3, continue skips the print statement, so 3 is not printed. All other numbers from 1 to 5 except 3 are printed.

🧠 Conceptual

advanced

Understanding while loop condition

What happens if the condition in a Swift while loop is initially false?

A The loop body runs once before checking the condition.

B The loop body never runs.

C The loop runs infinitely.

D The loop runs twice.

💡 Hint

Think about when the condition is checked in a while loop.

A while loop checks the condition before running the loop body. If the condition is false at the start, the loop body does not run at all.

❓ Predict Output

expert

Counting iterations in a while loop

What is the value of variable 'count' after running this Swift code?

Swift

var count = 0
var x = 10
while x > 0 {
    if x % 3 == 0 {
        x -= 2
    } else {
        x -= 1
    }
    count += 1
}

A 9

B 8

C 7

D 10

💡 Hint

Track how x changes each loop and count how many times the loop runs.

Starting from x=10, the loop decreases x by 1 if x is not divisible by 3, or by 2 if it is. Counting iterations until x <= 0 gives 7.

Practice

1. What does a while loop do in Swift?

easy

A. Repeats code while a condition is true

B. Runs code only once

C. Runs code a fixed number of times

D. Stops the program immediately

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop runs repeatedly as long as its condition stays true.

2. Step 2: Compare options with the definition

   Only Repeats code while a condition is true correctly describes repeating code while a condition is true.

3. Final Answer:

   Repeats code while a condition is true -> Option A

4. Quick Check:

   While loop = repeat while true condition [OK]

Hint: While loops run as long as condition is true [OK]

Common Mistakes:

• Thinking while loops run a fixed number of times
• Confusing while with if statements
• Assuming while loops run only once

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

easy

A. while condition: { /* code */ }

B. while (condition) do { /* code */ }

C. while { condition } /* code */

D. while condition { /* code */ }

Solution

1. Step 1: Recall Swift while loop syntax

   Swift uses: while condition { code } without parentheses or extra keywords.

2. Step 2: Check each option

   while condition { /* code */ } matches Swift syntax exactly; others have extra keywords or wrong punctuation.

3. Final Answer:

   while condition { /* code */ } -> Option D

4. Quick Check:

   Swift while syntax = while condition { } [OK]

Hint: Swift while loops use no parentheses around condition [OK]

Common Mistakes:

• Adding parentheses around the condition
• Using 'do' keyword incorrectly
• Using colon instead of braces

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

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

medium

A. 1 2 3

B. 3 2 1

C. 3 2 1 0

D. 0 1 2 3

Solution

1. Step 1: Analyze the loop condition and variable

   Variable count starts at 3 and loop runs while count > 0.

2. Step 2: Trace each iteration

   Prints 3, then count becomes 2; prints 2, count 1; prints 1, count 0; loop stops.

3. Final Answer:

   3 2 1 -> Option B

4. Quick Check:

   Loop prints count down from 3 to 1 [OK]

Hint: Count down from 3 to 1, stops before 0 [OK]

Common Mistakes:

• Including 0 in output
• Printing in ascending order
• Not decreasing count inside loop

4. Identify the error in this Swift code:

var i = 1
while i < 5 {
    print(i)
}

medium

A. Variable i should be a constant

B. Incorrect while syntax

C. Missing increment of i inside the loop

D. print statement is invalid

Solution

1. Step 1: Check loop structure and variable changes

   The loop condition depends on i, but i never changes inside the loop.

2. Step 2: Understand effect of missing increment

   Without increasing i, the condition i < 5 stays true forever, causing an infinite loop.

3. Final Answer:

   Missing increment of i inside the loop -> Option C

4. Quick Check:

   Loop variable must change to avoid infinite loop [OK]

Hint: Always update loop variable inside while loop [OK]

Common Mistakes:

• Forgetting to increment or change loop variable
• Thinking print causes error
• Assuming syntax is wrong

5. How can you use a while loop to sum all even numbers from 2 to 10 inclusive in Swift?

hard

A. Use a variable starting at 2, add it to sum, increment by 2 until 10

B. Start at 1, add all numbers, then multiply by 2

C. Use a while loop with condition i <= 10, increment i by 2, add i

D. Use a while loop starting at 10, increment 2 each time, add to sum

Solution

1. Step 1: Plan loop to add even numbers from 2 to 10

   Start with i = 2, add i to sum, then increase i by 2 to get next even number.

2. Step 2: Check options for correct approach

   Use a variable starting at 2, add it to sum, increment by 2 until 10 correctly describes starting at 2, adding to sum, incrementing by 2 until 10.

3. Final Answer:

   Use a variable starting at 2, add it to sum, increment by 2 until 10 -> Option A

4. Quick Check:

   Sum evens by stepping 2 from 2 to 10 [OK]

Hint: Increment by 2 to sum even numbers quickly [OK]

Common Mistakes:

• Incrementing by 2 without starting at 2
• Starting from 10 and incrementing
• Multiplying sum incorrectly