Data types (Int, Double, String, Bool) in iOS Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an Int in Swift?

An Int is a data type that stores whole numbers without decimals, like 5 or -10.

beginner

How does Double differ from Int?

Double stores numbers with decimals, like 3.14, while Int stores whole numbers only.

beginner

What kind of values does Bool hold?

Bool holds only two values: true or false. It is used for yes/no or on/off decisions.

beginner

What is a String in Swift?

String is a data type that stores text, like words or sentences, for example: "Hello" or "Swift".

intermediate

Why is it important to use the correct data type in Swift?

Using the correct data type helps the app use memory efficiently and prevents errors by making sure data is handled properly.

Which Swift data type would you use to store the number 42?

A Bool

B Int

C String

D Double

42 is a whole number, so Int is the correct data type.

Which data type can hold the value 3.14159?

A Double

B Int

C Bool

D String

Double stores decimal numbers like 3.14159.

What value can a Bool variable hold?

A Any number

B Text only

C true or false

D Decimal numbers

Bool holds only true or false.

Which data type would you use to store the word "Hello"?

A String

B Bool

C Int

D Double

String stores text like "Hello".

Why should you choose the right data type in Swift?

A To make the app slower

B It does not matter

C To confuse other developers

D To use memory efficiently and avoid errors

Correct data types help the app run smoothly and prevent mistakes.

Explain the difference between Int and Double in Swift.

Think about numbers with and without decimals.

Describe when you would use a Bool and a String in an app.

Consider yes/no questions and words.

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