Int, Double, Float number types in Swift

Introduction

We use Int, Double, and Float to store numbers in Swift. Each type helps us keep different kinds of numbers, like whole numbers or numbers with decimals.

When you need to count things like apples or books (use Int).

When you want to store precise decimal numbers like money or measurements (use Double).

When you want to save memory and can accept less precision for decimal numbers (use Float).

Syntax

Swift

var wholeNumber: Int = 10
var decimalNumber: Double = 3.14
var smallerDecimal: Float = 2.5

Int stores whole numbers without decimals.

Double stores decimal numbers with high precision.

Float stores decimal numbers but with less precision and uses less memory.

Examples

This stores a whole number representing age.

Swift

var age: Int = 25

This stores a precise decimal number for pi.

Swift

var pi: Double = 3.14159

This stores a decimal number for temperature with less precision.

Swift

var temperature: Float = 36.6

You can let Swift guess the type if you assign a value directly.

Swift

var count = 100 // Swift infers this as Int

Sample Program

This program counts apples and calculates total cost using Int and Double types. It shows how to convert Int to Double for calculation.

Swift

import Foundation

var apples: Int = 5
var pricePerApple: Double = 0.99
var totalCost: Double = Double(apples) * pricePerApple

print("You bought \(apples) apples.")
print("Each apple costs $\(pricePerApple).")
print("Total cost is $\(totalCost).")

Important Notes

You cannot directly multiply Int and Double without converting one type to the other.

Double is preferred for most decimal numbers because it is more precise than Float.

Use Int when you only need whole numbers to save memory and avoid decimals.

Summary

Int stores whole numbers.

Double stores precise decimal numbers.

Float stores decimal numbers with less precision and uses less memory.

Practice

1.

Which Swift type is best to store the number 42 without any decimal part?

easy

A. String

B. Double

C. Float

D. Int

Solution

1. Step 1: Understand the number type

   The number 42 is a whole number without decimals.

2. Step 2: Match with Swift types

   Int stores whole numbers, while Double and Float store decimal numbers.

3. Final Answer:

   Int -> Option D

4. Quick Check:

   Whole number = Int [OK]

Hint: Whole numbers use Int, decimals use Double or Float [OK]

Common Mistakes:

• Choosing Double or Float for whole numbers
• Confusing String with number types

2.

Which of the following is the correct way to declare a variable price as a Double with value 19.99 in Swift?

?

easy

A. var price: Int = 19.99

B. var price = 19.99f

C. var price: Double = 19.99

D. var price: Float = "19.99"

Solution

1. Step 1: Check type and value compatibility

   Double can store decimal numbers like 19.99 correctly.

2. Step 2: Validate syntax

   var price: Double = 19.99 uses correct syntax: variable name, type annotation, and decimal value.

3. Final Answer:

   var price: Double = 19.99 -> Option C

4. Quick Check:

   Double declaration syntax = var name: Double = value [OK]

Hint: Use var name: Double = value for decimals [OK]

Common Mistakes:

• Using 'f' suffix which is invalid in Swift
• Assigning decimal to Int type
• Using quotes for numbers

3.

What will be the output of this Swift code?

let a: Float = 3.14
let b: Double = 3.14
print(a == b)

medium

A. false

B. true

C. Compile-time error

D. Runtime error

Solution

1. Step 1: Understand type comparison

   Float and Double are different types; comparing them directly requires conversion.

2. Step 2: Check equality operation

   Swift allows comparing Float and Double, but values may differ due to precision, so a == b is false.

3. Final Answer:

   false -> Option A

4. Quick Check:

   Float vs Double equality = false [OK]

Hint: Float and Double differ in precision; direct equality often false [OK]

Common Mistakes:

• Assuming Float and Double are equal if values look same
• Expecting compile error for comparing different types

4.

Identify the error in this Swift code snippet:

var x: Int = 10.5
var y: Float = 20

medium

A. Cannot assign integer 20 to Float variable

B. Cannot assign decimal 10.5 to Int variable

C. Missing semicolon after variable declarations

D. Variable names are invalid

Solution

1. Step 1: Check variable type and assigned value

   Variable x is Int but assigned 10.5 which is a decimal number.

2. Step 2: Validate other assignments

   Variable y is Float and assigned 20 (an integer), which is allowed by implicit conversion.

3. Final Answer:

   Cannot assign decimal 10.5 to Int variable -> Option B

4. Quick Check:

   Int cannot hold decimals [OK]

Hint: Int variables cannot hold decimal values [OK]

Common Mistakes:

• Thinking Float cannot hold integer values
• Expecting semicolons in Swift
• Assuming variable names are invalid

5.

You want to store the value 0.123456789 in Swift with the highest precision possible. Which type should you choose and why?

hard

A. Double, because it stores decimal numbers with more precision

B. Float, because it uses less memory

C. Int, because it stores whole numbers accurately

D. String, to keep exact digits

Solution

1. Step 1: Understand precision needs

   The number 0.123456789 has many decimal places requiring high precision.

2. Step 2: Compare Swift types for precision

   Double stores decimal numbers with more precision than Float; Int stores whole numbers only.

3. Step 3: Consider String

   String stores text, not numbers, so it cannot be used for numeric calculations.

4. Final Answer:

   Double, because it stores decimal numbers with more precision -> Option A

5. Quick Check:

   Highest decimal precision = Double [OK]

Hint: Use Double for precise decimal numbers [OK]

Common Mistakes:

• Choosing Float for high precision decimals
• Using Int for decimal numbers
• Using String for numeric calculations