Int, Double, Float number types in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code with mixed number types?

Consider the following Swift code snippet. What will be printed when it runs?

Swift

let a: Int = 5
let b: Double = 3.2
let c = Double(a) + b
print(c)

A 8.2

B 8

C Type error at compile time

D 5.32

💡 Hint

Remember that you need to convert Int to Double before adding.

The Int value 5 is converted to Double 5.0, then added to 3.2, resulting in 8.2.

❓ Predict Output

intermediate

What is the value of variable 'result' after this Swift code runs?

Look at this Swift code. What is the value of 'result'?

Swift

let x: Float = 2.5
let y: Double = 4.5
let result = Double(x) * y
print(result)

A Type mismatch error

B 11.25f

C 7.0

D 11.25

💡 Hint

Float must be converted to Double before multiplication.

Float 2.5 is converted to Double 2.5, multiplied by 4.5, resulting in 11.25.

❓ Predict Output

advanced

What error does this Swift code produce?

Examine this Swift code snippet. What error will it cause when compiled?

Swift

let a: Int = 10
let b: Float = 3.5
let c = a + b
print(c)

A Prints 13.5

B Prints 13

C Type error: Cannot add Int and Float directly

D Runtime error: nil value

💡 Hint

Swift does not allow adding Int and Float without conversion.

You must convert either Int to Float or Float to Int before adding; otherwise, compiler error occurs.

🧠 Conceptual

advanced

Which Swift type is best for precise decimal calculations?

You want to store currency values in Swift with exact decimal precision. Which type should you use?

A Float

B Decimal

C Int

D Double

💡 Hint

Floating point types can cause rounding errors.

Decimal type is designed for precise decimal arithmetic, ideal for currency.

❓ Predict Output

expert

How many items are in the resulting array after this Swift code runs?

Analyze this Swift code and determine the number of elements in 'results'.

Swift

let numbers: [Double] = [1.0, 2.5, 3.7, 4.0]
let results = numbers.compactMap { num -> Int? in
    let intValue = Int(num)
    return num == Double(intValue) ? intValue : nil
}
print(results.count)

A 2

B 3

C 1

D 4

💡 Hint

compactMap filters out nil values after checking if Double equals Int conversion.

Only 1.0 and 4.0 are whole numbers; 2.5 and 3.7 are filtered out, so count is 2.

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