If and if-else statements in Swift - Mini Project: Build & Apply

If and if-else statements

📖 Scenario: You are creating a simple app that checks the temperature outside and gives advice on what to wear.

🎯 Goal: Build a program that uses if and if-else statements to decide what message to show based on the temperature.

📋 What You'll Learn

Create a variable to store the temperature as an integer

Create a variable to store a temperature limit

Use an if statement to check if the temperature is below the limit

Use an if-else statement to print different messages based on the temperature

💡 Why This Matters

🌍 Real World

Apps often need to make decisions based on data, like weather apps telling you what to wear.

💼 Career

Understanding <code>if</code> and <code>if-else</code> statements is essential for controlling program flow in any software development job.

1

DATA SETUP: Create a temperature variable

Create a variable called temperature and set it to 15.

Swift

// Create a variable called temperature and set it to 15
// Your code here

Hint

Use var to create a variable and assign the number 15 to temperature.

2

CONFIGURATION: Create a temperature limit variable

Create a variable called limit and set it to 20.

Swift

var temperature = 15
// Create a variable called limit and set it to 20
// Your code here

Hint

Use var to create a variable named limit and assign it the value 20.

3

CORE LOGIC: Use an if statement to check temperature

Write an if statement that checks if temperature is less than limit. Inside the if, write a comment // It's cold.

Swift

var temperature = 15
var limit = 20
// Write an if statement to check if temperature is less than limit
// Inside the if, add a comment // It's cold
// Your code here

Hint

Use if temperature < limit { } and put the comment inside the braces.

4

OUTPUT: Use if-else to print messages

Write an if-else statement that checks if temperature is less than limit. If true, print "Wear a jacket". Otherwise, print "No jacket needed".

Swift

var temperature = 15
var limit = 20
if temperature < limit {
    // It's cold
}
// Write an if-else statement to print the correct message
// Your code here

Hint

Use if temperature < limit { print("Wear a jacket") } else { print("No jacket needed") }.

Practice

1. What does an if statement do in Swift?

easy

A. It runs code only if a condition is true.

B. It repeats code multiple times.

C. It stores data in a variable.

D. It defines a new function.

Solution

1. Step 1: Understand the purpose of if statement

   An if statement checks a condition and runs code only when that condition is true.

2. Step 2: Compare with other options

   Repeating code is done by loops, storing data is done by variables, and defining functions uses func.

3. Final Answer:

   It runs code only if a condition is true. -> Option A

4. Quick Check:

   If statement = runs code if true [OK]

Hint: If checks true condition to run code, else skips it [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if stores data
• Mixing if with function definitions

2. Which of the following is the correct syntax for an if-else statement in Swift?

easy

A. if condition { } else { }

B. if (condition) then { } else { }

C. if condition then { } else { }

D. if condition: { } else: { }

Solution

1. Step 1: Recall Swift if-else syntax

   Swift uses if condition { } and else { } blocks without extra keywords like 'then' or colons.

2. Step 2: Check each option

   if condition { } else { } matches Swift syntax exactly. Options A, B, and C use invalid keywords or punctuation.

3. Final Answer:

   if condition { } else { } -> Option A

4. Quick Check:

   Swift if-else = if condition { } else { } [OK]

Hint: Swift uses braces {} without 'then' or colons in if-else [OK]

Common Mistakes:

• Adding 'then' keyword
• Using colons after if or else
• Putting condition in parentheses unnecessarily

3. What will be printed by this Swift code?

let number = 10
if number > 5 {
    print("Big")
} else {
    print("Small")
}

medium

A. Small

B. No output

C. 10

D. Big

Solution

1. Step 1: Evaluate the condition

   The variable number is 10. The condition number > 5 is true because 10 is greater than 5.

2. Step 2: Determine which block runs

   Since the condition is true, the code inside the if block runs, printing "Big".

3. Final Answer:

   Big -> Option D

4. Quick Check:

   10 > 5 is true, so prints "Big" [OK]

Hint: Check condition true? Run if block, else run else block [OK]

Common Mistakes:

• Confusing which block runs
• Printing variable instead of string
• Ignoring condition result

4. Find the error in this Swift code:

let age = 18
if age >= 18
    print("Adult")
else
    print("Minor")

medium

A. Variable age should be a string

B. Wrong comparison operator

C. Missing braces { } around if and else blocks

D. No error, code is correct

Solution

1. Step 1: Check Swift if-else syntax

   Swift requires braces { } around the code blocks after if and else.

2. Step 2: Identify missing braces

   The code lacks braces after if age >= 18 and else, causing a syntax error.

3. Final Answer:

   Missing braces { } around if and else blocks -> Option C

4. Quick Check:

   Swift needs braces for if-else blocks [OK]

Hint: Always use { } after if and else in Swift [OK]

Common Mistakes:

• Omitting braces in if-else
• Using wrong operators
• Wrong variable types

5. You want to write Swift code that prints "Positive", "Negative", or "Zero" depending on the value of an integer variable num. Which code correctly uses if-else statements to do this?

hard

A. if num >= 0 {
print("Positive")
} else if num <= 0 {
print("Negative")
} else {
print("Zero")
}

B. if num > 0 {
print("Positive")
} else if num < 0 {
print("Negative")
} else {
print("Zero")
}

C. if num > 0 {
print("Positive")
} else {
print("Negative")
}
print("Zero")

D. if num == 0 {
print("Zero")
} else if num > 0 {
print("Negative")
} else if num < 0 {
print("Positive")
}

Solution

1. Step 1: Understand the conditions needed

   We need to check if num is greater than 0, less than 0, or exactly 0.

2. Step 2: Analyze each option

   if num > 0 { print("Positive") } else if num < 0 { print("Negative") } else { print("Zero") } correctly checks >0, then <0, else zero. if num >= 0 { print("Positive") } else if num <= 0 { print("Negative") } else { print("Zero") } wrongly overlaps conditions. if num > 0 { print("Positive") } else { print("Negative") } print("Zero") prints "Zero" always. if num == 0 { print("Zero") } else if num > 0 { print("Negative") } else if num < 0 { print("Positive") } incorrectly prints "Negative" for positive numbers and "Positive" for negative numbers.

3. Final Answer:

   if num > 0 { print("Positive") } else if num < 0 { print("Negative") } else { print("Zero") } -> Option B

4. Quick Check:

   Check >0, else if <0, else zero [OK]

Hint: Check positive first, then negative, else zero last [OK]

Common Mistakes:

• Overlapping conditions causing wrong output
• Printing zero outside else block
• Wrong order of conditions