Ternary conditional operator in Swift - Mini Project: Build & Apply

Using the Ternary Conditional Operator in Swift

📖 Scenario: Imagine you are building a simple app that checks if a person is old enough to vote. You want to decide if the person can vote or not based on their age.

🎯 Goal: You will create a program that uses the ternary conditional operator to decide if a person is eligible to vote. The program will print "Can vote" if the person is 18 or older, and "Cannot vote" if younger.

📋 What You'll Learn

Create a variable called age with the value 20

Create a variable called votingStatus that uses the ternary conditional operator to check if age is 18 or more

Use the ternary conditional operator with the condition age >= 18

Set votingStatus to "Can vote" if true, otherwise "Cannot vote"

Print the value of votingStatus

💡 Why This Matters

🌍 Real World

Ternary operators help make quick decisions in code, like checking user age for permissions or showing different messages.

💼 Career

Understanding ternary operators is useful for writing clean and concise code in app development and many programming tasks.

1

Create the age variable

Create a variable called age and set it to the integer value 20.

Swift

# Create a variable called age and set it to 20
# Your code here

Hint

Use var age = 20 to create the variable.

2

Create the votingStatus variable using the ternary operator

Create a variable called votingStatus that uses the ternary conditional operator with the condition age >= 18. Set it to "Can vote" if true, otherwise "Cannot vote".

Swift

var age = 20
# Create votingStatus using ternary operator to check if age >= 18
# Your code here

Hint

Use the syntax condition ? valueIfTrue : valueIfFalse.

3

Use the ternary operator in a simple expression

Make sure the variable votingStatus uses the ternary conditional operator with the exact condition age >= 18 and the exact values "Can vote" and "Cannot vote".

Swift

var age = 20
var votingStatus = age >= 18 ? "Can vote" : "Cannot vote"
# Confirm the ternary operator is used correctly
# Your code here

Hint

Check that the ternary operator uses the condition age >= 18 exactly.

4

Print the votingStatus

Write a print statement to display the value of the variable votingStatus.

Swift

var age = 20
var votingStatus = age >= 18 ? "Can vote" : "Cannot vote"
# Print the votingStatus variable
# Your code here

Hint

Use print(votingStatus) to show the result.

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