Comparison operators in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained comparison operators

What is the output of this Swift code snippet?

Swift

let a = 5
let b = 10
let c = 15
print(a < b && b < c)

A true

B false

C Compilation error

D Runtime error

💡 Hint

Think about how logical AND works with comparison operators.

The expression checks if a is less than b AND b is less than c. Both are true, so the result is true.

❓ Predict Output

intermediate

Result of equality and inequality operators

What will be printed by this Swift code?

Swift

let x = 7
let y = 7
print(x == y, x != y)

A true false

B false true

C true true

D false false

💡 Hint

Check if x and y are equal or not.

x == y is true because both are 7; x != y is false because they are equal.

❓ Predict Output

advanced

Output of mixed comparison and logical operators

What is the output of this Swift code?

Swift

let p = 3
let q = 6
let r = 9
print(p < q || q > r && r == 9)

A Runtime error

B false

C Compilation error

D true

💡 Hint

Remember operator precedence: && before ||.

q > r && r == 9 is false && true = false; p < q || false = true || false = true.

❓ Predict Output

advanced

Output of comparing optional values

What will this Swift code print?

Swift

let a: Int? = nil
let b: Int? = 5
print(a == b)

A Compilation error

B false

C true

D Runtime error

💡 Hint

Comparing nil to a value returns false.

Optional values can be compared; nil is not equal to 5, so false is printed.

❓ Predict Output

expert

Output of custom Comparable struct comparison

Given this Swift code, what is the output?

Swift

struct Box: Comparable {
    let volume: Int
    static func < (lhs: Box, rhs: Box) -> Bool {
        lhs.volume < rhs.volume
    }
}
let box1 = Box(volume: 10)
let box2 = Box(volume: 20)
print(box1 > box2)

A true

B Runtime error

C false

D Compilation error

💡 Hint

The > operator uses the < operator logic reversed.

box1.volume (10) is not greater than box2.volume (20), so false is printed.

Practice

1. Which of the following comparison operators checks if two values are equal in Swift?

easy

A. ==

B. !=

C. >

D. <=

Solution

1. Step 1: Understand the equality operator

   The operator == is used to check if two values are equal in Swift.

2. Step 2: Compare with other operators

   != means not equal, > means greater than, and <= means less than or equal to.

3. Final Answer:

   == -> Option A

4. Quick Check:

   Equality operator = == [OK]

Hint: Remember: double equals means equality check [OK]

Common Mistakes:

• Confusing == with = (assignment)
• Using != to check equality
• Mixing > and < with equality

2. Which of the following is the correct syntax to check if variable a is not equal to variable b in Swift?

easy

A. a != b

B. a =! b

C. a !== b

D. a <> b

Solution

1. Step 1: Identify the not equal operator in Swift

   Swift uses != to check if two values are not equal.

2. Step 2: Check syntax correctness

   a != b is correct. a =! b is invalid syntax, !== is for identity comparison in some languages but not for value inequality in Swift, and <> is not a Swift operator.

3. Final Answer:

   a != b -> Option A

4. Quick Check:

   Not equal operator = != [OK]

Hint: Not equal always has ! before = [OK]

Common Mistakes:

• Swapping = and ! in != operator
• Using === instead of !=
• Using <> which is not valid in Swift

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

let x = 10
let y = 20
print(x > y)

medium

A. true

B. 10

C. 20

D. false

Solution

1. Step 1: Understand the comparison

   The code compares if x (10) is greater than y (20).

2. Step 2: Evaluate the comparison

   Since 10 is not greater than 20, the expression x > y is false.

3. Final Answer:

   false -> Option D

4. Quick Check:

   10 > 20 = false [OK]

Hint: Compare values carefully, > means strictly greater [OK]

Common Mistakes:

• Assuming 10 > 20 is true
• Confusing > with <
• Printing variable values instead of boolean

4. Identify the error in the following Swift code snippet:

let a = 5
let b = 10
if a = b {
    print("Equal")
} else {
    print("Not Equal")
}

medium

A. Using print instead of println

B. Missing parentheses around condition

C. Using = instead of == in if condition

D. Variables a and b must be var, not let

Solution

1. Step 1: Check the if condition syntax

   The condition uses a = b, which is assignment, not comparison.

2. Step 2: Correct operator for comparison

   To compare values, Swift requires == instead of =.

3. Final Answer:

   Using = instead of == in if condition -> Option C

4. Quick Check:

   Comparison needs ==, not = [OK]

Hint: Use == for comparison, = is assignment [OK]

Common Mistakes:

• Using = instead of == in conditions
• Thinking parentheses are mandatory in Swift if
• Confusing print and println functions

5. You want to check if a number n is between 10 and 20 inclusive in Swift. Which of the following expressions correctly uses comparison operators to do this?

hard

A. n > 10 || n < 20

B. n >= 10 && n <= 20

C. n == 10 && n == 20

D. n != 10 && n != 20

Solution

1. Step 1: Understand the range condition

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

2. Step 2: Analyze each option

   n >= 10 && n <= 20 uses n >= 10 && n <= 20, which correctly checks the inclusive range. n > 10 || n < 20 uses OR which is incorrect for range. n == 10 && n == 20 checks if n equals both 10 and 20 simultaneously, which is impossible. n != 10 && n != 20 checks if n is not 10 and not 20, which does not ensure the range.

3. Final Answer:

   n >= 10 && n <= 20 -> Option B

4. Quick Check:

   Inclusive range uses >= and <= with AND [OK]

Hint: Use && with >= and <= for inclusive range checks [OK]

Common Mistakes:

• Using || instead of && for range
• Checking equality to both ends at once
• Using != which excludes values instead of range