Int, Long, Float, Double number types in Kotlin

Introduction

We use different number types to store numbers in the best way for our program. Each type holds numbers of different sizes and with or without decimals.

When you need to store whole numbers that fit in a small range, use Int.

When you need to store very big whole numbers, use Long.

When you need to store numbers with decimals and less precision, use Float.

When you need to store numbers with decimals and more precision, use Double.

When you want to save memory by choosing the smallest type that fits your number.

Syntax

Kotlin

val myInt: Int = 123
val myLong: Long = 1234567890123L
val myFloat: Float = 12.34F
val myDouble: Double = 12.3456789

Use L suffix for Long numbers to tell Kotlin it is a Long.

Use F suffix for Float numbers to tell Kotlin it is a Float.

Examples

This stores a whole number without decimals in an Int variable.

Kotlin

val age: Int = 30

This stores a very large whole number using Long. The L is needed.

Kotlin

val distance: Long = 9876543210L

This stores a decimal number with less precision using Float. The F is needed.

Kotlin

val price: Float = 19.99F

This stores a decimal number with more precision using Double.

Kotlin

val pi: Double = 3.1415926535

Sample Program

This program shows how to declare and print Int, Long, Float, and Double variables.

Kotlin

fun main() {
    val myInt: Int = 100
    val myLong: Long = 10000000000L
    val myFloat: Float = 10.5F
    val myDouble: Double = 10.123456789

    println("Int value: $myInt")
    println("Long value: $myLong")
    println("Float value: $myFloat")
    println("Double value: $myDouble")
}

Important Notes

Int and Long store whole numbers only, no decimals.

Float and Double store decimal numbers, but Double is more precise.

Always use suffix L for Long and F for Float to avoid errors.

Summary

Int is for normal whole numbers.

Long is for very big whole numbers.

Float is for decimal numbers with less precision.

Double is for decimal numbers with more precision.

Practice

1. Which Kotlin number type should you use to store a whole number like 42?

easy

A. Float

B. Double

C. Int

D. Long

Solution

1. Step 1: Understand the number type categories

   Int is used for normal whole numbers without decimals.

2. Step 2: Match the number 42 to the type

   42 is a whole number and fits in Int range.

3. Final Answer:

   Int -> Option C

4. Quick Check:

   Whole number 42 = Int [OK]

Hint: Whole numbers without decimals use Int by default [OK]

Common Mistakes:

• Choosing Float or Double for whole numbers
• Using Long unnecessarily for small numbers

2. Which of the following is the correct way to declare a Float variable with value 3.14 in Kotlin?

easy

A. val pi: Float = 3.14

B. val pi: Float = 3.14Ff

C. val pi: Float = 3.14d

D. val pi: Float = 3.14f

Solution

1. Step 1: Recall Kotlin Float literal syntax

   Float literals require an 'f' or 'F' suffix to distinguish from Double.

2. Step 2: Check each option

   val pi: Float = 3.14f uses '3.14f' which is correct. val pi: Float = 3.14 misses the suffix. val pi: Float = 3.14Ff has invalid suffix 'Ff'. val pi: Float = 3.14d uses 'd' which is for Double.

3. Final Answer:

   val pi: Float = 3.14f -> Option D

4. Quick Check:

   Float literals end with 'f' [OK]

Hint: Add 'f' suffix to decimal for Float type [OK]

Common Mistakes:

• Omitting 'f' suffix for Float literals
• Using 'd' suffix which is for Double
• Using invalid suffixes like 'Ff'

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

val a: Int = 100000
val b: Long = 10000000000L
val c: Float = 3.14f
val d: Double = 3.1415926535
println("$a $b $c $d")

medium

A. 100000 10000000000 3.1400001 3.1415926535

B. 100000 10000000000 3.14 3.1415926535

C. 100000 10000000000 3.14f 3.1415926535

D. 100000 10000000000 3.14 3.1415927

Solution

1. Step 1: Understand variable types and precision

   a is Int (100000), b is Long (10000000000L), c is Float (3.14f), d is Double (3.1415926535).

2. Step 2: Check printed values and precision

   Float prints as 3.1400001 due to precision limits, Double prints full precision (3.1415926535). So output matches 100000 10000000000 3.1400001 3.1415926535.

3. Final Answer:

   100000 10000000000 3.1400001 3.1415926535 -> Option A

4. Quick Check:

   Float prints with slight precision difference [OK]

Hint: Float prints decimals with limited precision [OK]

Common Mistakes:

• Thinking Float prints exactly 3.14
• Confusing Float and Double precision
• Misreading Long large number formatting

4. Identify the error in this Kotlin code snippet:

val bigNumber: Long = 12345678901234567890
val smallNumber: Int = 2147483648

medium

A. Both numbers are too large for their types

B. Only bigNumber is too large for Long

C. No errors, code is correct

D. Only smallNumber is too large for Int

Solution

1. Step 1: Check Long value range

   Long can hold values up to 9,223,372,036,854,775,807. The bigNumber literal exceeds this, so it causes an error.

2. Step 2: Check Int value range

   Int max is 2,147,483,647. The smallNumber is 2,147,483,648 which is 1 more than max, so it causes an error.

3. Step 3: Analyze the code

   Both literals are too large for their types, causing compile errors.

4. Final Answer:

   Both numbers are too large for their types -> Option A

5. Quick Check:

   Int max 2147483647, Long max 9223372036854775807; both exceeded [OK]

Hint: Check max values: Int max 2,147,483,647; Long max 9,223,372,036,854,775,807 [OK]

Common Mistakes:

• Ignoring suffix 'L' for Long literals
• Assuming Long can hold any big number
• Not checking Int max value

5. You want to store the population of a country which is about 1.4 billion people. Which Kotlin type is best and why?

Options:
A) Long because it can store very large whole numbers
B) Int because it stores whole numbers
C) Float because it stores decimal numbers
D) Double because it stores decimal numbers with more precision

hard

A. Int because it stores whole numbers

B. Long because it can store very large whole numbers

C. Float because it stores decimal numbers

D. Double because it stores decimal numbers with more precision

Solution

1. Step 1: Understand the population size and type limits

   Population is about 1.4 billion (1,400,000,000). Int max is 2,147,483,647, so Int can hold it.

2. Step 2: Consider best practice for large numbers

   Though Int can hold 1.4 billion, Long is safer for very large whole numbers and future growth.

3. Step 3: Decide on the best type

   Long is best because it can store very large whole numbers beyond Int range.

4. Final Answer:

   Long because it can store very large whole numbers -> Option B

5. Quick Check:

   Long preferred for large integers like population [OK]

Hint: Use Long for very large whole numbers like population [OK]

Common Mistakes:

• Choosing Int without considering future growth
• Using Float or Double for whole numbers unnecessarily
• Ignoring future growth beyond Int range