Comparison operators in Kotlin

Introduction

Comparison operators help us check if values are equal or which one is bigger or smaller. This is useful to make decisions in programs.

Checking if a user entered the correct password

Comparing ages to see who is older

Finding out if a number is positive or negative

Deciding if a score is high enough to pass

Sorting items by size or price

Syntax

Kotlin

a == b  // equals
 a != b  // not equals
 a > b   // greater than
 a < b   // less than
 a >= b  // greater than or equal to
 a <= b  // less than or equal to

Use double equals (==) to check if two values are the same.

Use != to check if two values are different.

Examples

This checks if x and y are equal. They are not, so it prints false.

Kotlin

val x = 5
val y = 10
println(x == y)  // false

This checks if a and b are different. They are the same, so it prints false.

Kotlin

val a = 7
val b = 7
println(a != b)  // false

This checks if age is at least 18. It is, so it prints true.

Kotlin

val age = 18
println(age >= 18)  // true

This checks if score is less than 50. It is not, so it prints false.

Kotlin

val score = 75
println(score < 50)  // false

Sample Program

This program checks if the temperature is hot, cold, or exactly 30 degrees using comparison operators.

Kotlin

fun main() {
    val temperature = 30
    val isHot = temperature > 25
    val isCold = temperature < 15
    println("Is it hot? $isHot")
    println("Is it cold? $isCold")
    println("Is temperature exactly 30? ${temperature == 30}")
}

Important Notes

Comparison operators return a Boolean value: true or false.

Use parentheses {} inside strings to show the result of comparisons.

Summary

Comparison operators help compare two values.

They return true or false depending on the comparison.

Common operators: ==, !=, >, <, >=, <=.

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