Comparison operators in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the == operator do in Kotlin?

The == operator checks if two values are equal in content. It compares the values, not their memory addresses.

intermediate

What is the difference between == and === in Kotlin?

== checks if two objects have the same value (content equality). === checks if two references point to the exact same object (reference equality).

beginner

List the basic comparison operators in Kotlin.

The basic comparison operators are: == (equal), != (not equal), < (less than), <= (less than or equal), > (greater than), >= (greater than or equal).

beginner

What is the result type of comparison operators in Kotlin?

Comparison operators return a Boolean value: true if the comparison is correct, false otherwise.

intermediate

How can you compare two strings ignoring case in Kotlin?

Use the function equals(other, ignoreCase = true) to compare two strings without considering letter case.

Which operator checks if two variables have the same value in Kotlin?

A !=

B ===

C <=

D ==

The == operator checks if two variables have the same value (content equality).

What does the === operator check in Kotlin?

A If two references point to the same object

B If one value is greater than another

C If two values are not equal

D If two values are equal

The === operator checks if two references point to the exact same object (reference equality).

What type of value do comparison operators return in Kotlin?

A Int

B String

C Boolean

D Double

Comparison operators return a Boolean value: true or false.

Which operator means 'not equal' in Kotlin?

A !=

B ==

C <=

D >=

The != operator means 'not equal' in Kotlin.

How do you compare two strings ignoring case in Kotlin?

A Use <code>==</code>

B Use <code>equals(other, ignoreCase = true)</code>

C Use <code>===</code>

D Use <code>!=</code>

Use equals(other, ignoreCase = true) to compare strings ignoring case.

Explain the difference between == and === operators in Kotlin.

Think about comparing what is inside versus comparing the actual object.

List all basic comparison operators in Kotlin and what they do.

Think about how you compare numbers or values in daily life.

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