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

Recall & Review

beginner

What is an Int in Swift?

An Int is a whole number without any decimal part. It can be positive, negative, or zero, like 5, -3, or 0.

beginner

What is the difference between Double and Float in Swift?

Double stores decimal numbers with more precision (more digits after the decimal) than Float. Double uses 64 bits, Float uses 32 bits.

intermediate

Why choose Double over Float?

Choose Double when you need more accurate decimal numbers, like in money calculations or measurements.

beginner

How do you declare a variable of type Int in Swift?

Use var number: Int = 10 to declare an integer variable named number with value 10.

beginner

What happens if you try to store a decimal number in an Int variable?

You get an error because Int cannot hold decimal numbers. You must use Double or Float for decimals.

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

A Double

B Int

C Float

D String

42 is a whole number, so Int is the best choice.

Which type has more precision for decimal numbers?

A Double

B Int

C Float

D Bool

Double uses 64 bits and stores more precise decimal numbers than Float.

What will happen if you assign 3.14 to an Int variable?

A It causes a compile-time error

B It stores 3 only

C It stores 3.14 correctly

D It converts to a string

Int cannot hold decimals, so Swift gives a compile-time error.

Which type uses 32 bits to store numbers?

A Int

B Double

C Float

D Bool

Float uses 32 bits, Double uses 64 bits.

Why might you prefer Double over Float?

A Double stores whole numbers only

B Double is faster

C Double uses less memory

D Double has higher precision

Double stores decimal numbers more precisely than Float.

Explain the differences between Int, Double, and Float in Swift.

Think about whole vs decimal numbers and precision.

When should you use Double instead of Float in your Swift programs?

Consider accuracy and size of numbers.

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