# Conditionals & Logic

### `if` Statement

An `if` statement executes a code block when its condition evaluates to `true`. If the condition is `false`, the code block does not execute.

```var halloween = true
if halloween {  print("Trick or treat!")}
// Prints: Trick or treat!
```

### `else` Statement

An `else` statement is a partner to an `if` statement. When the condition for the `if` statement evaluates to `false`, the code within the body of the `else` will execute.

```var turbulence = false
if turbulence {  print("Please stay seated.")} else {  print("You may freely move around.")}
// Prints: You may freely move around.```

### `else if` Statement

An `else if` statement provides additional conditions to check for within a standard `if`/`else` statement. `else if` statements can be chained and exist only after an `if` statement and before an `else`.

```var weather = "rainy"
if weather == "sunny" {  print("Grab some sunscreen")} else if weather == "rainy" {  print("Grab an umbrella")} else if weather == "snowing" {  print("Wear your snow boots")} else {  print("Invalid weather")}
// Prints: Grab an umbrella```

### Comparison Operators

Comparison operators compare the values of two operands and return a Boolean result:

• `<` less than
• `>` greater than
• `<=` less than or equal to
• `>=` greater than or equal to
• `==` equal to
• `!=` not equal to
`5 > 1       // true 6 < 10      // true 2 >= 3      // false3 <= 5      // true"A" == "a"  // false"B" != "b"  // true`

### Ternary Conditional Operator

The ternary conditional operator, denoted by a `?`, creates a shorter alternative to a standard `if`/`else` statement. It evaluates a single condition and if `true`, executes the code before the `:`. If the condition is `false`, the code following the `:` is executed.

```var driverLicense = true
driverLicense ? print("Driver's Seat") : print("Passenger's Seat")
// Prints: Driver's Seat```

### `switch` Statement

The `switch` statement is a type of conditional used to check the value of an expression against multiple cases. A `case` executes when it matches the value of the expression. When there are no matches between the `case` statements and the expression, the `default` statement executes.

```var secondaryColor = "green"
switch secondaryColor {  case "orange":    print("Mix of red and yellow")  case "green":    print("Mix of blue and yellow")  case "purple":    print("Mix of red and blue")   default:     print("This might not be a secondary color.") }
// Prints: Mix of blue and yellow```

### `switch` Statement: Interval Matching

Intervals within a `switch` statement’s `case` provide a range of values that are checked against an expression.

```let year = 1905var artPeriod: String
switch year {  case 1860...1885:    artPeriod = "Impressionism"  case 1886...1910:    artPeriod = "Post Impressionism"  case 1912...1935:     artPeriod = "Expressionism"  default:      artPeriod = "Unknown"}
// Prints: Post Impressionism```

### `switch` Statement: Compound Cases

A compound case within a `switch` statement is a single `case` that contains multiple values. These values are all checked against the `switch` statement’s expression and are separated by commas.

```let service = "Seamless"
switch service {  case "Uber", "Lyft":    print("Travel")  case "DoorDash", "Seamless", "GrubHub":    print("Restaurant delivery")  case "Instacart", "FreshDirect":    print("Grocery delivery")  default:     print("Unknown service")}
// Prints: Restaurant delivery```

### `switch` Statement: `where` Clause

Within a `switch` statement, a `where` clause is used to test additional conditions against an expression.

```let num = 7
switch num {  case let x where x % 2 == 0:    print("\(num) is even")  case let x where x % 2 == 1:    print("\(num) is odd")  default:    print("\(num) is invalid")}
// Prints: 7 is odd```

### Logical Operator `!`

The logical NOT operator, denoted by a `!`, is a prefix operator that negates the value on which it is prepended. It returns `false` when the original value is `true` and returns `true` when the original value is `false`.

```!true          // false!false         // true
```

### Logical Operator `&&`

The logical AND operator, denoted by an `&&`, evaluates two operands and returns a Boolean result. It returns `true` when both operands are `true` and returns `false` when at least one operand is `false`.

`true && true    // truetrue && false   // false false && true   // false false && false  // false`

### Logical Operator `||`

The logical OR operator, denoted by `||`, evaluates two operands and returns a Boolean result. It returns `false` when both operands are `false` and returns `true` when at least one operand is `true`.

```true || true    // truetrue || false   // truefalse || true   // true false || false  // false
```

### Combining Logical Operators

Logical operators can be chained in order to create more complex logical expressions. When logical operators are chained, it’s important to note that the `&&` operator has a higher precedence over the `||` operator and will get evaluated first.

```!false && true || false  // true
/* !false && true evaluates first and returns true. Then, the expression, true || false evaluates and returns the final result, true. */
false || true && false   // false
/* true && false evaluates first which returns false. Then, the expression, false || false evaluates and returns the final result, false. */ ```

### Controlling Order of Execution

Within a Swift logical expression, parentheses, `()`, can be used to organize and control the flow of operations. The usage of parentheses within a logical expression overrides operator precedence rules and improves code readability.

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