Swift - Control Flow

3 kinds of control flow

Loops
1. For-In
2. While
3. Repeat-While
Conditional Statement
1. If
2. Switch
Control Transfer Statements
1. continue
2. break
3. fallthrough
4. return
5. throw

For-In Loops

For-in loop is used to iterate over a sequence, such as items in an array, dictionary, Set, ranges of numbers, or characters in a string.

example :

let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names {
    print("Hello, \(name)!")
}

use stride(from:to:by:) or stride(from:through:by:) after in to partially loop over at different intervals.

For-In loop can be used to iterate any collection, including own classes and collection types, as long as those types conform to the Sequence protocol.

While Loops

use while loops when the number of iterations isn’t known before the first iteration begins.
two kinds of while loops:

while evaluates its condition at the start
repeat-while evaluates its condition at the end

If

It executes a set of statements only if that condition is true, If false then it executes the statements in else clause if any present. else clause is optional.

example :

temperatureInFahrenheit = 90
if temperatureInFahrenheit <= 32 {
    print("It's very cold. Consider wearing a scarf.")
} else if temperatureInFahrenheit >= 86 {
    print("It's really warm. Don't forget to wear sunscreen.")
} else {
    print("It's not that cold. Wear a t-shirt.")
}

multiple else clause can be chained together

Switch

A switch statement provides an alternative to the if statement for responding to multiple potential states. It takes a value and compares it against several possible matching patterns. It then executes an appropriate block of code

Every switch statement must be exhaustive. That is, every possible value of the type being considered must be matched by one of the switch cases. If it’s not appropriate to provide a case for every possible value, you can define a default case to

example :

let someCharacter: Character = "z"
switch someCharacter {
case "a":
    print("The first letter of the alphabet")
case "z":
    print("The last letter of the alphabet")
default:
    print("Some other character")
}

compound case can be used to combine 2 value in a case separated by comma.

example :

case "a", "A":
    print("The letter A")`

Values in switch cases can be a range

example : 
`case 0:
    naturalCount = "no"
case 1..<5:
    naturalCount = "a few"
case 5..<12:
    naturalCount = "several"

tuples can be used to test multiple values in the same switch statement. along with tuples underscore character (_), also known as the wildcard pattern, to match any possible value.

example :

switch somePoint {
case (0, 0):
    print("\(somePoint) is at the origin")
case (_, 0):
    print("\(somePoint) is on the x-axis")
case (0, _):
    print("\(somePoint) is on the y-axis")
default:
    print("\(somePoint) in plane")
}

Value Bindings - switch case can name the value or values it matches to temporary constants or variables, for use in the body of the case.

example :

switch somePoint {
case (let x, 0):
    print("on the x-axis with an x value of \(x)")
case (0, let y):
    print("on the y-axis with a y value of \(y)")
case let (x, y):
    print("somewhere else at (\(x), \(y))")
}

where clause can be used with switch to check for additional conditions.

example :

switch somePoint {
case let (x, y) where x == y:
    print("(\(x), \(y)) is on the line x == y")
case let (x, y) where x == -y:
    print("(\(x), \(y)) is on the line x == -y")
case let (x, y):
    print("(\(x), \(y)) is just some arbitrary point")
}

Compound cases can also include value bindings. All of the patterns of a compound case have to include the same set of value bindings

example :

switch somePoint {
case (let distance, 0), (0, let distance):
    print("On an axis, \(distance) from the origin")
default:
    print("Not on an axis")
}

Control Transfer Statements

Continue

continue statement stop current iteration of loop and start again at the beginning of the next iteration through the loop

Break

The break statement ends execution of an entire control flow statement immediately. It can be used in a switch or loop statement to exit early.

Fallthrough

It can be used inside the switch case body to jump into the next case without matching condition.

example :

switch integerToDescribe {
case 2, 3, 5, 7, 11, 13, 17, 19:
    description += " a prime number, and also"
    fallthrough
default:
    description += " an integer."
}

Labeled Statements

It can be used to break or continue nested loop / nested conditional statement.

example :

outerLoop : for element1 in array1{
    for element2 in array2{
        if(element1 == element2){
            continue outerLoop
        }
    }
    uniqueElemetsInArray1.append(element1)
}
print(uniqueElemetsInArray1)  //[21, 13, 5]