Ternary conditional operator in Swift

Introduction

The ternary conditional operator helps you choose between two values quickly based on a condition. It makes your code shorter and easier to read.

When you want to assign a value based on a simple yes/no question.

When you want to print one message if something is true, and another if it is false.

When you want to set a color or style depending on a condition.

When you want to return one of two values from a function quickly.

When you want to simplify an if-else statement that only picks between two options.

Syntax

Swift

condition ? valueIfTrue : valueIfFalse

The condition is a question that results in true or false.

If the condition is true, the operator returns valueIfTrue, otherwise it returns valueIfFalse.

Examples

This checks if age is 18 or more. If yes, canVote is "Yes", otherwise "No".

Swift

let age = 18
let canVote = age >= 18 ? "Yes" : "No"

Here, if score is 60 or more, grade is "Pass", else "Fail".

Swift

let score = 75
let grade = score >= 60 ? "Pass" : "Fail"

Depending on isSunny, it suggests what to take.

Swift

let isSunny = false
let weather = isSunny ? "Take sunglasses" : "Take umbrella"

Sample Program

This program checks if the temperature is above 25 degrees. If yes, it suggests wearing shorts; otherwise, pants.

Swift

import Foundation

let temperature = 30
let advice = temperature > 25 ? "Wear shorts" : "Wear pants"
print("Temperature: \(temperature)°C")
print("Advice: \(advice)")

Important Notes

Use the ternary operator only for simple conditions to keep code clear.

For complex decisions, prefer if-else statements for better readability.

Summary

The ternary operator chooses between two values based on a condition.

It is a shortcut for simple if-else assignments.

Use it to make your code shorter and easier to read when the choice is simple.

Practice

1. What does the ternary conditional operator do in Swift?
condition ? valueIfTrue : valueIfFalse

easy

A. Declares a constant value

B. Repeats a block of code multiple times

C. Defines a new function

D. Chooses one of two values based on a condition

Solution

1. Step 1: Understand the operator structure

   The ternary operator uses a condition followed by a question mark, then two values separated by a colon.

2. Step 2: Identify its purpose

   It selects the first value if the condition is true, otherwise the second value.

3. Final Answer:

   Chooses one of two values based on a condition -> Option D

4. Quick Check:

   Ternary operator = chooses between two values [OK]

Hint: Remember: condition ? trueValue : falseValue picks one [OK]

Common Mistakes:

• Confusing ternary with loops
• Thinking it declares variables
• Mixing it with function syntax

2. Which of the following is the correct syntax for the ternary conditional operator in Swift?

easy

A. condition ? valueIfTrue : valueIfFalse

B. condition : valueIfTrue ? valueIfFalse

C. condition ? (valueIfTrue, valueIfFalse)

D. condition ? valueIfTrue; valueIfFalse

Solution

1. Step 1: Recall the ternary syntax

   The correct syntax places the condition first, then a question mark, then the true value, a colon, and the false value.

2. Step 2: Compare options

   Only condition ? valueIfTrue : valueIfFalse matches this exact pattern.

3. Final Answer:

   condition ? valueIfTrue : valueIfFalse -> Option A

4. Quick Check:

   Syntax is condition ? true : false [OK]

Hint: Question mark before colon is key in ternary syntax [OK]

Common Mistakes:

• Swapping question mark and colon
• Using commas instead of colon
• Adding semicolons inside ternary

3. What is the output of this Swift code?

let age = 20
let canVote = age >= 18 ? "Yes" : "No"
print(canVote)

medium

A. No

B. Yes

C. true

D. false

Solution

1. Step 1: Evaluate the condition

   age is 20, which is greater than or equal to 18, so the condition is true.

2. Step 2: Apply ternary operator

   Since the condition is true, canVote is assigned "Yes".

3. Final Answer:

   Yes -> Option B

4. Quick Check:

   age >= 18 is true, so output is "Yes" [OK]

Hint: Check condition result first, then pick true or false value [OK]

Common Mistakes:

• Confusing true and false branches
• Assuming boolean output instead of string
• Ignoring the condition value

4. Identify the error in this Swift code using the ternary operator:

let score = 85
let grade = score > 90 ? "A" : "B" else "C"

medium

A. Using double quotes instead of single quotes

B. Missing parentheses around condition

C. Extra 'else' keyword after ternary operator

D. Incorrect variable declaration

Solution

1. Step 1: Analyze ternary operator usage

   The ternary operator already includes both true and false values separated by a colon; adding 'else' is invalid syntax.

2. Step 2: Identify the syntax error

   The 'else' keyword after the ternary expression causes a syntax error.

3. Final Answer:

   Extra 'else' keyword after ternary operator -> Option C

4. Quick Check:

   No 'else' after ternary operator [OK]

Hint: Ternary uses colon, never 'else' keyword [OK]

Common Mistakes:

• Adding 'else' after ternary
• Confusing ternary with if-else blocks
• Misplacing colons and question marks

5. Given a dictionary of student scores, use a ternary operator in Swift to create a new dictionary that marks each student as "Pass" if their score is 50 or more, otherwise "Fail".
What is the correct way to write this using dictionary comprehension?

let scores = ["Anna": 75, "Ben": 45, "Cara": 50]
let results = scores.mapValues { score in
    // Fill in here
}

hard

A. score >= 50 ? "Pass" : "Fail"

B. if score >= 50 { "Pass" } else { "Fail" }

C. score > 50 ? "Pass" : "Fail"

D. score >= 50 ? "Fail" : "Pass"

Solution

1. Step 1: Understand the condition for passing

   Students pass if their score is 50 or more, so condition is score >= 50.

2. Step 2: Apply ternary operator correctly

   Use ternary to return "Pass" if true, else "Fail".

3. Final Answer:

   score >= 50 ? "Pass" : "Fail" -> Option A

4. Quick Check:

   Use condition ? "Pass" : "Fail" for mapping [OK]

Hint: Use mapValues with ternary: condition ? trueVal : falseVal [OK]

Common Mistakes:

• Using if-else instead of ternary in mapValues
• Wrong comparison operator (>)
• Swapping Pass and Fail values