Swift: Conditionals & Logic

Conditionals & Logic in Swift:

Let’s begin with the Conditionals and Logic in Swift.

if Statement:

When the condition of an if statement is true, it executes a code block. So, the code block does not execute if the condition is false.

var morning = true 
if morning {
  print("Rise and Shine!")
// Prints: Rise and Shine!

else Statement:

An if statement has a partner in the form of an else statement. Therefore, the else statement’s code runs if the if statement’s condition evaluates to false.

var covid = false 
if covid {
  print("Stay at home.")
} else {
  print("You can enjoy outside freely.")
// Prints: You can enjoy outside freely.

else if Statement:

Within a standard if/else statement, an else if statement adds more requirements to check for. else if statements can chain and only occur after an if statement and before an else statement.

let number = 0

if (number > 0) {
    print("Number is positive.")

else if (number < 0) {
    print("Number is negative")

else {
    print("Number is 0.")

//Prints: Number is 0.

Comparison Operators:

Operators for comparison Return a Boolean result by comparing the values of two operands:

  • < less than
  • > greater than
  • <= less than or equal to
  • >= greater than or equal to
  • == equal to
  • != not equal to
1 > 10        // false 
1 < 10        // true 
1 >= 10       // false
1 <= 10       // true
"X" == "x"    // false
"Y" != "y"    // true

Ternary Conditional Operator:

The ternary conditional operator, indicated by a ?, is a shorter version of the if/else statement. It evaluates a single condition and executes the code preceding the : if it is true. On the other hand, the code after the : is executed if the condition is false.

var workExperience = true
workExperience ? print("Welcome as an Employee") : print("Welcome as an Intern")
// Prints: Welcome as an Employee

switch Statement:

The switch statement is a conditional that checks the value of an expression against a variety of different situations. When the value of the expression matches the case, it executes. The default statement can use when there are no matches between the case statements and the expression.

var info = ("Drake", 22)

switch info {
  case ("Drake", 22): 
    print("Drake is 22 years old")

  case ("Lisa", 21): 
    print("Lisa is 21 years old")

    print("Not known")

//Prints: Drake is 22 years old

Interval Matching in switch Statement:

Within the case of a switch statement, intervals provide a range of values that are compared to an expression.

 var episode = 2
 var villain: String
  switch episode {
   case 1...3:
    villain = "Emperor Palpatine"
   case 4...6:
    villain = "Darth Vader"
   case 7...9:
    villain = "Kylo Ren"
    villain = "Unknown"
// Prints: Emperor Palpatine

Compound Cases in switch Statement:

Within a switch statement, a compound case is a single case that has multiple values. So, these values are separated by commas and checked against the switch statement’s expression.

let country = "Fiji"
switch country {
  case "Russia", "New Zealand", "Fiji":
    print("Eastern Country")
  case "USA", "Argentina", "Tonga":
    print("Western Country")
    print("Unknown Country")
// Prints: Eastern Country

where Clause in switch Statement:

A where clause can use within a switch statement to test additional conditions against an expression.

let number = 6
switch number {
  case let a where a % 2 == 0:
    print("\(number) is even")
  case let a where a % 2 == 1:
    print("\(number) is odd")
    print("\(number) is invalid")
// Prints: 6 is even

Logical Operator !:

The logical NOT operator, symbolized by !, is a prefix operator that negates the value to which it is added. When the original value is true, it returns false, and when the original value is false, it returns true.

!false        // true
!true         // false

Logical Operator &&:

The logical AND operator denoted by && evaluates two operands and returns a Boolean result. When both operands are true, it returns true, if at least one operand is false, it returns false.

true && true    // true
true && false   // false 
false && true   // false 
false && false  // false

Logical Operator ||:

|| denotes the logical OR operator, that evaluates two operands and returns a Boolean result. When both operands are false, it returns false, and when at least one operand is true, it returns true.

true || true    // true
true || false   // true
false || true   // true 
false || false  // false

Combining Logical Operators:

Logical operators can chain together to create more complex logical expressions. It’s wise to note that when logical operators are chained, the && operator takes precedence over the || operator and is evaluated first.

true && true || !true  // true
true && true is the first one to evaluate and returns true. The expression true || !true then evaluates and returns true as the final result. 
!true || true && false   // false
true && false were evaluated first and returns false. Then the expression, !true || false evaluates and returns false as the final result. 

Controlling Order of Execution:

Parentheses, (), can use to organize and control the flow of operations within a Swift logical expression. Parentheses within a logical expression override operator precedence rules, making code more readable.

// Without parentheses:
true || !false && false || false      // true 
// With parentheses:
(true || !false) && (false || false)  // false 

Helpful Tools:

Here are some useful tools to help you along your journey!

Setting up an IDE (Integrated Development Environment) can be difficult for beginners. The Online Compiler will enable you to run your code inside your browser without the need to install an IDE. If you need a more detailed explanation of a specific topic, the best place to find answers is in the Official Documentation.

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