Arithmetic operators and overflow in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code with overflow?

Consider the following Swift code using overflow addition. What will be printed?

Swift

var maxUInt8: UInt8 = 255
maxUInt8 = maxUInt8 &+ 1
print(maxUInt8)

A 0

B 256

C 255

D Runtime error

💡 Hint

Think about what happens when an 8-bit unsigned integer goes beyond its max value.

UInt8 can hold values from 0 to 255. Using &+ adds with overflow, so 255 + 1 wraps around to 0.

❓ Predict Output

intermediate

What is the result of this subtraction with overflow?

What will this Swift code print when subtracting with overflow?

Swift

var minInt8: Int8 = -128
minInt8 = minInt8 &- 1
print(minInt8)

A 127

B -129

C -128

D Runtime error

💡 Hint

Remember Int8 ranges from -128 to 127 and &- allows wrapping.

Int8 minimum is -128. Subtracting 1 with &- wraps around to 127.

🔧 Debug

advanced

Why does this Swift code cause a runtime error?

This code tries to add two Int values. Why does it crash?

Swift

let a: Int = Int.max
let b: Int = 1
let c = a + b
print(c)

A Because Int.max is not a valid integer

B Because Int addition does not allow overflow and crashes on overflow

C Because b is not an Int

D Because print cannot print large integers

💡 Hint

Check what happens when adding 1 to the maximum Int value without overflow operators.

Swift's default Int addition traps on overflow, causing a runtime error when exceeding Int.max.

🧠 Conceptual

advanced

Which operator safely adds two UInt8 values allowing overflow?

Which Swift operator adds two UInt8 values and allows overflow without crashing?

A +

B -

C &+

D &-

💡 Hint

Look for the operator with an ampersand that allows overflow.

The &+ operator performs addition with overflow, wrapping around on overflow instead of crashing.

❓ Predict Output

expert

What is the output of this mixed overflow and normal addition code?

Analyze this Swift code and determine what it prints.

Swift

var x: UInt8 = 250
let y: UInt8 = 10
let z = x &+ y
let w = x + y
print(z)
print(w)

A

260
4

B

4
260

C

Runtime error
4

D

4
Runtime error

💡 Hint

Consider which addition allows overflow and which does not.

x &+ y wraps around: 250 + 10 = 260, which overflows UInt8 and wraps to 4.
Normal + causes runtime error on overflow.