Selection Statements

NOTE

Mr. Gordon generated this concept summary and the related exercises using the Claude Anthropic large language model.

He then edited the results for clarity, accuracy, and brevity.

Selection statements allow us to selectively run blocks of code when a given condition is true. Selection statements are also called conditional statements.

if Statements

An if statement allows you to execute code based on certain conditions.

Basic Syntax:

if condition {
    // Code to execute if condition is true
}

Example:

let temperature = 25
 
if temperature > 30 {
    print("It's hot outside!")
} else if temperature > 20 {
    print("It's a nice day!")
} else {
    print("It's a bit chilly.")
}

In this example, the program will print “It’s a nice day!” because the temperature is 25.

switch Statements

A switch statement allows you to check a value against multiple possible matching patterns, including ranges.

Basic Syntax:

switch someValue {
case value1:
    // Code to execute if someValue matches value1
case value2, value3:
    // Code to execute if someValue matches value2 or value3
case valueRange:
    // Code to execute if someValue falls within valueRange
default:
    // Code to execute if no other cases match
}

Example 1: Matching Specific Values

let dayOfWeek = "Wednesday"
 
switch dayOfWeek {
case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday":
    print("It's a weekday.")
case "Saturday", "Sunday":
    print("It's the weekend!")
default:
    print("Invalid day of the week.")
}

In this example, the program will print “It’s a weekday.” because the dayOfWeek is “Wednesday”.

Example 2: Matching Ranges

let temperature = 28
 
switch temperature {
case ...0:
    print("Freezing!")
case 1...10:
    print("Very cold")
case 11...20:
    print("Cool")
case 21...30:
    print("Warm")
case 31...:
    print("Hot!")
default:
    print("Invalid temperature")
}

This will print “Warm” because 28 falls within the range 21…30.

Example 3: Combining Ranges and Specific Values

let grade = 85
 
switch grade {
case 90...100:
    print("A")
case 80..<90:
    print("B")
case 70..<80:
    print("C")
case 60..<70:
    print("D")
case 0..<60:
    print("F")
case -1:
    print("Incomplete")
default:
    print("Invalid grade")
}

This will print “B” because 85 falls within the range 80..<90.

In these examples:

• ... is used for one-sided ranges (e.g., ...0 means “0 and below”, 31... means “31 and above”)
• ... is inclusive on both sides (e.g., 1...10 includes both 1 and 10)
• ..< is inclusive on the left and exclusive on the right (e.g., 80..<90 includes 80 but not 90)

These range operators make switch statements very powerful for handling numeric ranges in Swift.

Exercises

1. Ice Cream Flavour Checker

Write an if statement that checks a variable flavor and prints different messages based on the flavor:

• If it’s “chocolate”, print “Classic choice!”
• If it’s “vanilla”, print “Simple and delicious!”
• For any other flavor, print “Enjoy your ice cream!“

2. Age Group Categorizer

Create a switch statement that takes a person’s age as an integer and categorizes them into different life stages. Use ranges in your switch statement to handle the following categories:

• 0-2 years: “Infant”
• 3-12 years: “Child”
• 13-19 years: “Teenager”
• 20-39 years: “Young Adult”
• 40-59 years: “Middle-aged Adult”
• 60 years and above: “Senior”

Also, include a case for invalid ages (negative numbers). Test your code with various ages to ensure it works correctly. Here’s a starting point for your code:

let age = 25  // Change this value to test different ages
 
switch age {
    // Your code here
}