# Array Fields and Functions

Arrays have multiple built-in fields and functions that can be used to get information about and manipulate the contents of the array.

The field `length`, and the functions `concat`, and `contains` are available for both variable-sized and fixed-sized or variable-sized arrays.

```
  let length: Int
```

The number of elements in the array.

```
    // Declare an array of integers.
    let numbers = [42, 23, 31, 12]

    // Find the number of elements of the array.
    let length = numbers.length

    // `length` is `4`
```

```
  fun concat(_ array: T): T
```

Concatenates the parameter `array` to the end of the array the function is called on, but does not modify that array.

Both arrays must be the same type `T`.

This function creates a new array whose length is the sum of the length of the array the function is called on and the length of the array given as the parameter.

```
    // Declare two arrays of integers.
    let numbers = [42, 23, 31, 12]
    let moreNumbers = [11, 27]

    // Concatenate the array `moreNumbers` to the array `numbers`
    // and declare a new variable for the result.
    //
    let allNumbers = numbers.concat(moreNumbers)

    // `allNumbers` is `[42, 23, 31, 12, 11, 27]`
    // `numbers` is still `[42, 23, 31, 12]`
    // `moreNumbers` is still `[11, 27]`
```

```
  fun contains(_ element: T): Bool
```

Returns true if the given element of type `T` is in the array.

```
    // Declare an array of integers.
    let numbers = [42, 23, 31, 12]

    // Check if the array contains 11.
    let containsEleven = numbers.contains(11)
    // `containsEleven` is `false`

    // Check if the array contains 12.
    let containsTwelve = numbers.contains(12)
    // `containsTwelve` is `true`

    // Invalid: Check if the array contains the string "Kitty".
    // This results in a type error, as the array only contains integers.
    //
    let containsKitty = numbers.contains("Kitty")
```