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.

Practice

1. What happens in Swift when you add two Int8 numbers and the result exceeds the maximum value of Int8 without using overflow operators?

easy

A. The program causes a runtime error and stops.

B. The result wraps around automatically without error.

C. The result is set to zero.

D. Swift converts the result to a larger integer type automatically.

Solution

1. Step 1: Understand Int8 limits

   Int8 can hold values from -128 to 127. Adding beyond 127 causes overflow.

2. Step 2: Behavior without overflow operators

   Swift checks for overflow and triggers a runtime error if it happens without using special operators.

3. Final Answer:

   The program causes a runtime error and stops. -> Option A

4. Quick Check:

   Overflow without &+ causes error [OK]

Hint: Overflow without &+ causes runtime error in Swift [OK]

Common Mistakes:

• Thinking Swift wraps values automatically without &+
• Assuming Swift converts to bigger type automatically
• Believing result resets to zero on overflow

2. Which of the following is the correct syntax to add two UInt8 numbers allowing overflow in Swift?

easy

A. let result = a &+ b

B. let result = a ++ b

C. let result = a + b

D. let result = a add b

Solution

1. Step 1: Recall overflow operators in Swift

   Swift uses &+ for addition with overflow allowed.

2. Step 2: Check each option

   let result = a &+ b uses &+ correctly; others are invalid or normal addition without overflow.

3. Final Answer:

   let result = a &+ b -> Option A

4. Quick Check:

   Use &+ for overflow addition [OK]

Hint: Use &+ for overflow addition in Swift [OK]

Common Mistakes:

• Using + instead of &+ for overflow
• Using ++ which is invalid in Swift
• Trying non-existent operators like 'add'

3. What is the output of the following Swift code?

let maxValue: UInt8 = 255
let result = maxValue &+ 1
print(result)

medium

A. 256

B. Runtime error

C. 255

D. 0

Solution

1. Step 1: Understand UInt8 max value and overflow

   UInt8 max is 255. Adding 1 with &+ causes overflow wrapping to 0.

2. Step 2: Evaluate the code output

   Using &+ allows overflow, so 255 + 1 wraps to 0 without error.

3. Final Answer:

   0 -> Option D

4. Quick Check:

   UInt8 overflow wraps to 0 with &+ [OK]

Hint: &+ wraps UInt8 overflow to 0 [OK]

Common Mistakes:

• Expecting 256 which is out of UInt8 range
• Expecting runtime error without &+
• Thinking result stays 255

4. Identify the error in this Swift code snippet:

var x: Int8 = 120
x = x + 10
print(x)

medium

A. No error, prints 130

B. Syntax error: cannot assign to variable

C. Runtime error due to overflow

D. Compile-time error: type mismatch

Solution

1. Step 1: Check Int8 range and operation

   Int8 max is 127. Adding 10 to 120 results in 130, which is overflow.

2. Step 2: Understand Swift overflow behavior without &+

   Normal + operator causes runtime error on overflow.

3. Final Answer:

   Runtime error due to overflow -> Option C

4. Quick Check:

   Int8 overflow without &+ causes runtime error [OK]

Hint: Int8 overflow without &+ triggers runtime error [OK]

Common Mistakes:

• Assuming it prints 130 ignoring overflow
• Thinking it's a syntax or compile error
• Believing variable assignment is invalid

5. You want to safely multiply two Int8 numbers that might overflow. Which Swift code correctly handles overflow and prints the wrapped result?

let a: Int8 = 100
let b: Int8 = 2
// Fill in the blank
print(result)

hard

A. let result = a * b

B. let result = a &* b

C. let result = a *& b

D. let result = multiply(a, b)

Solution

1. Step 1: Recall overflow multiplication operator

   Swift uses &* to multiply with overflow allowed.

2. Step 2: Check options for correct syntax

   let result = a &* b uses &* correctly; others are invalid or normal multiplication without overflow.

3. Final Answer:

   let result = a &* b -> Option B

4. Quick Check:

   Use &* for overflow multiplication [OK]

Hint: Use &* to multiply with overflow in Swift [OK]

Common Mistakes:

• Using * instead of &* for overflow
• Using invalid operator *&
• Assuming a multiply() function exists