Int, Long, Float, Double number types in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Int type in Kotlin?

Int is a number type in Kotlin that stores whole numbers without decimals. It uses 32 bits and can hold values from -2,147,483,648 to 2,147,483,647.

beginner

How is Long different from Int in Kotlin?

Long is a number type that stores bigger whole numbers than Int. It uses 64 bits and can hold values from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.

beginner

What does the Float type represent in Kotlin?

Float is a number type for decimal numbers (numbers with fractions). It uses 32 bits and is less precise than Double. You write a Float number with an 'f' or 'F' at the end, like 3.14f.

beginner

Explain the Double type in Kotlin.

Double is a number type for decimal numbers with more precision than Float. It uses 64 bits and is the default type for decimal numbers in Kotlin.

beginner

How do you write a Long and a Float literal in Kotlin?

To write a Long number, add 'L' or 'l' at the end, like 123L. To write a Float number, add 'f' or 'F' at the end, like 3.14f.

Which Kotlin type would you use to store the number 5000000000?

A Long

B Int

C Float

D Double

5000000000 is too big for Int, so Long is the correct type.

What suffix do you add to a number to make it a Float in Kotlin?

A L

B f

C F64

D d

You add 'f' to make a number a Float, like 2.5f.

Which type is the default for decimal numbers in Kotlin?

A Int

B Long

C Float

D Double

Double is the default decimal type in Kotlin.

What is the size in bits of the Int type in Kotlin?

A 64 bits

B 16 bits

C 32 bits

D 128 bits

Int uses 32 bits to store whole numbers.

Which type can store the largest whole number?

A Long

B Float

C Int

D Double

Long can store larger whole numbers than Int.

Describe the differences between Int, Long, Float, and Double in Kotlin.

Think about size, precision, and whether the number has decimals.

How do you write literals for Long and Float types in Kotlin? Give examples.

Remember the suffix letters for each type.

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