While loop in Swift

Introduction

A while loop helps you repeat a set of actions as long as a condition is true. It saves you from writing the same code many times.

When you want to keep asking a user for input until they give a valid answer.

When you want to count up or down until a certain number is reached.

When you want to keep checking if a task is done before moving on.

When you want to repeat an action but don't know in advance how many times.

When you want to process items until a list is empty.

Syntax

Swift

while condition {
    // code to repeat
}

The condition is a true or false check.

The code inside the braces runs only if the condition is true.

Examples

This loop prints numbers 1 to 3. It stops when count becomes 4.

Swift

var count = 1
while count <= 3 {
    print("Count is \(count)")
    count += 1
}

This loop runs 5 times and then stops by changing the condition.

Swift

var keepGoing = true
var tries = 0
while keepGoing {
    print("Trying...")
    tries += 1
    if tries == 5 {
        keepGoing = false
    }
}

Sample Program

This program counts down from 5 to 1 and then prints "Blast off!".

Swift

import Foundation

var number = 5
while number > 0 {
    print("Countdown: \(number)")
    number -= 1
}
print("Blast off!")

Important Notes

Make sure the condition will eventually become false, or the loop will run forever.

You can change the condition inside the loop to stop it when needed.

Summary

A while loop repeats code while a condition is true.

It is useful when you don't know how many times you need to repeat.

Always check that the loop will stop at some point.

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