Control-Flow.md

Control Flow

If Expressions

The if expression is used to control the execution of code based on a condition. It starts with if followed by a boolean and a block of code in {}. No parantheses () is needed around the boolean value.

It can be followed by any number of else if's, and optionally end with an else.

if a == 1 {
    print("a is 1")
} else if a == 2 {
    print("a is 2")
} else {
    print("a is something else")
}

An if expression returns the value of the last line of the executed branch. If that branch is empty or does not exist, it will return null.

let x_string = if x == 1 {
    "one"
} else if x == 2 {
    "two"
}
// x_string is "one" if x is 1, "two" if x is 2, and otherwise null

Loops

While Loops

A while loop allows the repeated execution of a block of code while a condition is true. It starts with while followed by a boolean and a block of code in {}. No parantheses () is needed around the boolean value.

let a = 0;
while a < 10 {
    print("a is less than 10")
    a += 1
}

The break statement can be used to exit the loop immediately.

let condition_met = false
// This loop will loop twice, exiting on the second time
while true {
    if condition_met {
        break
    }
    condition_met = true
}

For loops

A for loop facilitates iterating over elements of a collection, such as iterating through an array. It uses the following syntax, where arr is the collection to iterate, and elem is the corresponding element in arr each iteration.

let arr = [1, 2, 3]
for elem in arr {
    print(elem)
}

It is identical to the following while loop, but much more simple.

let arr = [1, 2, 3]
let index = 0
while index < 3 {
    print(arr[index])
    index += 1
}

To iterate through a range of integers, we use the operations ... and ... Given two integers m and n, m...n creates the collection of integers between m to n, inclusive, in ascending order . m..n creates the same numbers but excluding n.

for i in 0...3 {
    print(i)
}
// 0
// 1
// 2
// 3

for i in 0..3 {
    print(i)
}
// 0
// 1
// 2