Bool type and logical operators in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code using logical AND?

Consider the following Swift code snippet. What will be printed when it runs?

Swift

let a = true
let b = false
print(a && b)

A false

B true

C nil

D Compilation error

💡 Hint

Remember that logical AND (&&) returns true only if both sides are true.

The logical AND operator returns true only if both operands are true. Here, 'a' is true but 'b' is false, so the result is false.

❓ Predict Output

intermediate

What does this Swift code print using logical OR?

Look at this Swift code. What will be the output?

Swift

let x = false
let y = true
print(x || y)

A true

B false

C nil

D Runtime error

💡 Hint

Logical OR (||) returns true if at least one operand is true.

Since 'y' is true, the OR operation returns true regardless of 'x'.

❓ Predict Output

advanced

What is the output of this Swift code with combined logical operators?

Analyze this Swift code and determine what it prints.

Swift

let p = true
let q = false
let r = true
print(p && q || r)

A Compilation error

B false

C true

D nil

💡 Hint

Remember the precedence: && is evaluated before ||.

First, p && q is false (true && false = false). Then false || r is true (false || true = true).

❓ Predict Output

advanced

What does this Swift code print using the NOT operator?

What is the output of this Swift code snippet?

Swift

let flag = false
print(!flag)

A false

B Syntax error

C nil

D true

💡 Hint

The NOT operator (!) reverses the Boolean value.

Since flag is false, !flag is true.

🧠 Conceptual

expert

How many items are in the resulting dictionary after this Swift code runs?

Consider this Swift code that uses Boolean keys in a dictionary. How many key-value pairs does the dictionary contain after execution?

Swift

var dict = [Bool: String]()
dict[true] = "Yes"
dict[false] = "No"
dict[true] = "Maybe"

A 1

B 2

C 3

D 0

💡 Hint

Dictionary keys must be unique. Assigning a value to an existing key replaces the old value.

The dictionary has two keys: true and false. The value for true is updated from "Yes" to "Maybe", so total pairs remain 2.

Practice

1. Which of the following is a valid Boolean value in Swift?

easy

A. 0

B. 1

C. yes

D. true

Solution

1. Step 1: Understand Boolean values in Swift

   Swift uses true and false as Boolean values, not numbers or words.

2. Step 2: Identify the valid Boolean value

   Among the options, only true is a valid Boolean value.

3. Final Answer:

   true -> Option D

4. Quick Check:

   Boolean values are true or false [OK]

Hint: Remember: Bool values are only true or false [OK]

Common Mistakes:

• Confusing 1 or 0 as Boolean values
• Using words like 'yes' or 'no' instead of true/false

2. Which of the following is the correct way to write a logical AND operation in Swift?

easy

A. a && b

B. a & b

C. a and b

D. a || b

Solution

1. Step 1: Recall Swift logical AND syntax

   Swift uses && for logical AND, not a single ampersand or words.

2. Step 2: Identify the correct syntax

   a && b uses &&, which is the correct logical AND operator.

3. Final Answer:

   a && b -> Option A

4. Quick Check:

   Logical AND in Swift is && [OK]

Hint: Use double ampersand && for AND in Swift [OK]

Common Mistakes:

• Using single & instead of &&
• Writing 'and' as a word
• Confusing AND with OR operator ||

3. What is the output of the following Swift code?

let a = true
let b = false
print(a || b && !a)

medium

A. Syntax error

B. false

C. true

D. nil

Solution

1. Step 1: Evaluate the NOT operator

   !a means NOT true, which is false.

2. Step 2: Evaluate AND operation

   b && !a is false && false, which is false.

3. Step 3: Evaluate OR operation

   a || (result of AND) is true || false, which is true.

4. Final Answer:

   true -> Option C

5. Quick Check:

   Logical operators follow precedence: NOT, AND, OR [OK]

Hint: Remember operator precedence: ! before && before || [OK]

Common Mistakes:

• Ignoring operator precedence
• Evaluating OR before AND
• Confusing !a as true

4. Identify the error in the following Swift code:

let x = true
let y = false
let result = x & y

medium

A. Missing semicolon at the end of the line

B. Using single & instead of && for logical AND

C. Variables x and y must be integers

D. Using let instead of var for result

Solution

1. Step 1: Check logical AND operator usage

   In Swift, logical AND uses &&, not a single &.

2. Step 2: Identify the syntax error

   Using & causes a compile error because it's a bitwise operator, not logical.

3. Final Answer:

   Using single & instead of && for logical AND -> Option B

4. Quick Check:

   Logical AND requires &&, not & [OK]

Hint: Use && for logical AND, & is bitwise [OK]

Common Mistakes:

• Confusing bitwise & with logical &&
• Thinking semicolons are required in Swift
• Assuming let cannot be used for constants

5. You want to check if a number is between 10 and 20 (inclusive) using Boolean logic in Swift. Which expression correctly uses logical operators to do this?

let number = 15
// Which condition is correct?

hard

A. number >= 10 && number <= 20

B. number > 10 || number < 20

C. number >= 10 || number <= 20

D. number > 10 && number < 20

Solution

1. Step 1: Understand the range condition

   To check if number is between 10 and 20 inclusive, it must be greater or equal to 10 AND less or equal to 20.

2. Step 2: Analyze each option

   number >= 10 && number <= 20 uses && with inclusive comparisons, which is correct. Others use OR or exclusive comparisons, which are incorrect.

3. Final Answer:

   number >= 10 && number <= 20 -> Option A

4. Quick Check:

   Use AND to combine both range checks [OK]

Hint: Use && to combine both conditions for range checks [OK]

Common Mistakes:

• Using || instead of && for range
• Using > or < instead of >= or <=
• Mixing OR and AND incorrectly