### Introduction to Swift

Swift: Basics
Swift: Variables
Swift: Conditionals & Logic
Swift: Logical Operators
Swift: Loops
Swift: Arrays
Swift: Sets
Swift: Dictionaries
Swift: Functions
Swift: Structures
Swift: Classes

# Swift: The for-in Loop

## for-in Loop in Swift:

Let’s start with the for-in loop in Swift now that we know what loops can do for us. The general syntax is as follows:

``````for variable in sequence {
for-in loop body
}``````

Iterating over a sequence of values, such as Strings (a sequence of characters) or ranges, is done with for-in loops (sequence of numbers). We use the closed range operator (`...`) with a lower bound number and an upper bound number to make a range. For example, the numbers 1, 2, and 3 are contained in a range of `1...3` with a lower bound of 1 and an upper bound of 3.

Let’s say we wanted to use a for-in loop to iterate (repeat tasks) while going through the range: `4...7`, which represents the sequence of numbers 4, 5, 6, and 7.

``````print("Why is 4 frightened of 5? Because...");
for numbers in 4...7 {
print(numbers);
}``````

Let’s analyse the above example:

• The loop starts with the `for` keyword.
• The current iteration’s value is stored in a variable named as `numbers`. It’s worth noting that we don’t declare it with a keyword like `var`; instead, the Swift compiler does it for us. It can be thought of as a placeholder, as the placeholder (`numbers`) has a value of `4` during the first iteration.
• The placeholder is separate from the iteration sequence by the `in` keyword.
• The sequence we’re iterating over is `4...7`, which is a range containing the numbers `4`, `5`, `6`, and `7`.
• Curly braces `{}` encircle the body of the `for``in` loop.

After considering the syntax, it should come as no surprise that our code snippet prints out:

``````Why is 4 frightened of 5? Because...
4
5
6
7``````

Do you get it? It’s because 5 sounds like fire too. Now, let’s get back to programmingâ€¦ ðŸ˜…