Comparison operators in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained comparison operators

What is the output of this Kotlin code snippet?

Kotlin

fun main() {
    val a = 5
    val b = 10
    val c = 15
    println(a < b && b < c)
}

A false

B true

C Compilation error

D Runtime exception

💡 Hint

Think about how logical AND works with comparison operators.

The expression 'a < b && b < c' 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 identity operators

What will be printed by this Kotlin code?

Kotlin

fun main() {
    val x = "hello"
    val y = "hello"
    println(x == y)
    println(x === y)
}

A true\nfalse

B false\nfalse

C false\ntrue

D true\ntrue

💡 Hint

Remember the difference between '==' and '===' in Kotlin.

'==' checks structural equality (content), so x == y is true. '===' checks referential equality (same object). Since both are identical string literals, they refer to the same instance in the constant pool, so true.

❓ Predict Output

advanced

Output of comparison with nullable types

What is the output of this Kotlin code?

Kotlin

fun main() {
    val a: Int? = null
    val b: Int? = 5
    println(a < b)
}

A Compilation error

B true

C false

D Runtime exception

💡 Hint

Kotlin's type system prevents direct comparisons involving nullable types.

Kotlin does not define comparison operators like '<' for nullable types (Int?) because they do not implement Comparable. This results in a compilation error.

❓ Predict Output

advanced

Output of custom compareTo implementation

Given this Kotlin class and code, what is printed?

Kotlin

class Box(val size: Int) : Comparable<Box> {
    override fun compareTo(other: Box): Int = this.size - other.size
}

fun main() {
    val box1 = Box(3)
    val box2 = Box(5)
    println(box1 < box2)
}

A Compilation error

B false

C true

D Runtime exception

💡 Hint

Check how the compareTo function affects the '<' operator.

The '<' operator uses compareTo. Since 3 - 5 is negative, box1 < box2 is true.

🧠 Conceptual

expert

Behavior of comparison operators with floating-point NaN

In Kotlin, what is the result of comparing a Double.NaN with any number using '<' or '>' operators?

A Both '<' and '>' return false when comparing NaN with any number

B '<' returns true and '>' returns false when comparing NaN with any number

C '<' returns false and '>' returns true when comparing NaN with any number

D Both '<' and '>' throw a runtime exception when comparing NaN with any number

💡 Hint

Recall how IEEE floating-point standard treats NaN in comparisons.

According to IEEE rules, any comparison with NaN using '<' or '>' returns false, no exception is thrown.

Practice

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

easy

A. <=

B. !=

C. >

D. ==

Solution

1. Step 1: Understand the meaning of comparison operators

   In Kotlin, the operator == is used to check if two values are equal.

2. Step 2: Identify the correct operator for equality

   The operator == returns true if both values are equal, otherwise false.

3. Final Answer:

   == -> Option D

4. Quick Check:

   Equality operator = == [OK]

Hint: Remember: '==' means equal, '!=' means not equal [OK]

Common Mistakes:

• Confusing '==' with '=' which is assignment
• Using '!=' to check equality
• Mixing up '>' and '<=' operators

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

easy

A. a != b

B. a <> b

C. a =! b

D. a !== b

Solution

1. Step 1: Recall Kotlin syntax for inequality

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

2. Step 2: Verify each option

   a != b is correct; a <> b is invalid in Kotlin; a =! b is incorrect syntax; a !== b checks referential inequality, not value inequality.

3. Final Answer:

   a != b -> Option A

4. Quick Check:

   Not equal operator = != [OK]

Hint: Use '!=' for not equal, never '<>' in Kotlin [OK]

Common Mistakes:

• Using '<>' which is not valid in Kotlin
• Swapping '=' and '!' in 'a =! b'
• Confusing '!=' with '!==', which checks references

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

val x = 10
val y = 20
println(x > y)

medium

A. false

B. true

C. 10

D. Compilation error

Solution

1. Step 1: Evaluate the comparison expression

   The expression x > y compares if 10 is greater than 20, which is false.

2. Step 2: Understand the println output

   Printing the boolean result of the comparison will output false.

3. Final Answer:

   false -> Option A

4. Quick Check:

   10 > 20 = false [OK]

Hint: Compare values carefully; 10 is not greater than 20 [OK]

Common Mistakes:

• Assuming 10 > 20 is true
• Confusing output with variable values
• Expecting a number instead of boolean output

4. Identify the error in this Kotlin code snippet:

val a = 5
val b = 10
if (a = b) {
    println("Equal")
} else {
    println("Not Equal")
}

medium

A. Variables a and b must be mutable

B. Missing semicolon after println

C. Using '=' instead of '==' in if condition

D. Incorrect println syntax

Solution

1. Step 1: Check the if condition syntax

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

2. Step 2: Correct the operator for comparison

   Use == to compare values, so it should be a == b.

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 '=' in if condition instead of '=='
• Thinking semicolons are required in Kotlin
• Assuming val variables must be mutable for comparison

5. Given the Kotlin code below, what will be the output?

val a = 7
val b = 7
val c = 10
println((a == b) && (b < c))

hard

A. false

B. true

C. 7

D. Compilation error

Solution

1. Step 1: Evaluate the first comparison (a == b)

   Since both a and b are 7, a == b is true.

2. Step 2: Evaluate the second comparison (b < c)

   Since 7 is less than 10, b < c is true.

3. Step 3: Evaluate the logical AND

   Both conditions are true, so true && true is true.

4. Final Answer:

   true -> Option B

5. Quick Check:

   (7 == 7) && (7 < 10) = true [OK]

Hint: Both conditions must be true for && to return true [OK]

Common Mistakes:

• Confusing && with || operator
• Misreading comparison results
• Expecting numeric output instead of boolean