Data types (Int, Double, String, Bool) in iOS Swift

Introduction

Data types help us tell the app what kind of information we want to store, like numbers, words, or true/false answers.

When you want to store a whole number like age or count.

When you need to store decimal numbers like price or temperature.

When you want to store text like a name or message.

When you want to store a true or false value like if a switch is on or off.

Syntax

iOS Swift

var number: Int = 10
var price: Double = 9.99
var name: String = "Alice"
var isOn: Bool = true

Int is for whole numbers without decimals.

Double is for numbers with decimals.

String is for text inside double quotes.

Bool is for true or false values.

Examples

This stores the whole number 25 as an integer.

iOS Swift

var age: Int = 25

This stores a decimal number for temperature.

iOS Swift

var temperature: Double = 36.6

This stores text inside quotes.

iOS Swift

var greeting: String = "Hello!"

This stores a false value for a login status.

iOS Swift

var isLoggedIn: Bool = false

Sample App

This app shows four pieces of information using different data types. It displays age as a whole number, price with decimals, a name as text, and a true/false status as Yes or No.

iOS Swift

import SwiftUI

struct ContentView: View {
    let age: Int = 30
    let price: Double = 19.99
    let name: String = "Bob"
    let isOn: Bool = true

    var body: some View {
        VStack(spacing: 20) {
            Text("Age: \(age)")
            Text("Price: $\(price)")
            Text("Name: \(name)")
            Text("Is On: \(isOn ? "Yes" : "No")")
        }
        .font(.title)
        .padding()
    }
}

@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

Important Notes

You can change the value of variables if you use var, but constants with let cannot be changed.

Use the correct data type to avoid errors and make your app work smoothly.

Strings must always be inside double quotes.

Summary

Int stores whole numbers.

Double stores decimal numbers.

String stores text inside quotes.

Bool stores true or false values.

Practice

1. Which Swift data type is used to store true or false values?

easy

A. Int

B. Double

C. String

D. Bool

Solution

1. Step 1: Understand the data types

   Bool stores true or false values, Int stores whole numbers, String stores text, and Double stores decimal numbers.

2. Step 2: Match the description to the type

   Since the question asks for true or false values, the correct type is Bool.

3. Final Answer:

   Bool -> Option D

4. Quick Check:

   Bool = true/false [OK]

Hint: True/false values always use Bool type [OK]

Common Mistakes:

• Confusing Bool with Int
• Using String for true/false
• Choosing Double for boolean values

2. Which of the following is the correct way to declare a Double variable named price with value 9.99 in Swift?

easy

A. var price: Double = 9.99

B. var price = "9.99"

C. var price Double = 9.99

D. var price: Int = 9.99

Solution

1. Step 1: Check variable declaration syntax

   In Swift, to declare a variable with a specific type, use var name: Type = value.

2. Step 2: Identify the correct type and value

   Since 9.99 is a decimal number, the type must be Double. var price: Double = 9.99 correctly declares price as Double with 9.99.

3. Final Answer:

   var price: Double = 9.99 -> Option A

4. Quick Check:

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

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

Common Mistakes:

• Assigning decimal to Int
• Using quotes for numbers
• Omitting type when needed

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

let number: Int = 5
let text: String = "5"
let isEqual = (number == Int(text)!)
print(isEqual)

medium

A. true

B. false

C. 5

D. Compilation error

Solution

1. Step 1: Understand the code logic

   number is an Int with value 5, text is a String "5". Int(text) converts the string "5" to integer 5.

2. Step 2: Compare values

   number == Int(text) compares 5 == 5, which is true. So isEqual is true and print outputs true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   5 == 5 is true [OK]

Hint: Convert String to Int before comparing [OK]

Common Mistakes:

• Comparing Int and String directly
• Forgetting Int(text) conversion
• Expecting string output

4. Identify the error in this Swift code snippet:

var isActive: Bool = "true"
print(isActive)

medium

A. print() cannot print Bool values

B. Bool cannot be assigned a String value

C. Variable name is invalid

D. Missing semicolon at end of line

Solution

1. Step 1: Analyze variable assignment

   isActive is declared as Bool but assigned the string "true" (in quotes), which is incorrect.

2. Step 2: Understand type mismatch

   Bool must be assigned true or false without quotes. Assigning a String causes a type error.

3. Final Answer:

   Bool cannot be assigned a String value -> Option B

4. Quick Check:

   Bool = true/false only, no quotes [OK]

Hint: Bool values are true or false without quotes [OK]

Common Mistakes:

• Using quotes around true/false
• Expecting semicolon error
• Thinking print can't show Bool

5. You want to store a user's age, height in meters, full name, and whether they are a student. Which Swift data types should you use for these variables respectively?

hard

A. String, String, Int, Bool

B. Double, Int, Bool, String

C. Int, Double, String, Bool

D. Bool, Int, Double, String

Solution

1. Step 1: Match each data to its type

   Age is a whole number -> Int, height with decimals -> Double, full name is text -> String, student status true/false -> Bool.

2. Step 2: Verify option matches order

   Int, Double, String, Bool lists Int, Double, String, Bool in that order, matching the variables correctly.

3. Final Answer:

   Int, Double, String, Bool -> Option C

4. Quick Check:

   Whole number, decimal, text, true/false [OK]

Hint: Match data meaning: whole, decimal, text, true/false [OK]

Common Mistakes:

• Mixing Int and Double
• Using Bool for text
• Confusing order of types