CSC1110 - Arrays

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    layout: true
    class: taylor msoe
    ---
    class: center, middle

.title[
      # Arrays
    ]

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---
    # Arrays
    * A way to store a group of the same-typed values

--
    * A way of parameterizing a variable name

--
    * Suppose we have three quiz scores stored as `int`s

``` Java
    int sum = quiz1 + quiz2 + quiz3;
    int average = (quiz1 + quiz2 + quiz3) / 3.0;
    ```

--
    * What if we have 100 quiz scores?

---
    # Array Basics
    * We declare an array reference as `int[] array`

--
    * The array has one property: `array.length`

--
    * Here we set `array` to point to an array literal:

``` Java
    array = {1, 2, 3, 4};
    ```

--
    * Alternatively, we can allocate space for an array:

``` Java
    array = new int[4];
    ```

---
    # Accessing Elements
    * We access elements with the subscript operator
    ``` Java
    int[] array = new int[4];
    array[0] = 1;
    array[1] = 2;
    array[2] = array[1] + 1;
    array[3] = array.length;
    ```

--
    * The array now contains: 1, 2, 3, 4

--
    * `array` is a parameterized variable name that uses the `[ ]` operator to select specific value

---
    # Examples
    ``` Java
    private static int sum(int[] scores) {
        int sum = 0;
        for (int i = 0; i < scores.length; i++) {
            sum += scores[i];
        }
        return sum;
    }

// scores.length must be greater than zero
    private static double average(int[] scores) {
        int sum = 0;
        for (int i = 0; i < scores.length; i++) {
            sum += scores[i];
        }
        return (double)sum / scores.length;
    }
    ```

---
    # Notes
    * You must use a valid parameter when subscripting, e.g., `array[-2]` will crash your program

--
    * Can have arrays of primitives or of references
        + `int[] integers = new int[5];`
        + `String[] words = new String[5];`
    --
    * Initial value for primitives is `0`, for references is `null`

--
    * Arrays cannot be resized

---
    # Adding a value to an array
    ``` Java
    // Returns an array that is one longer than words containing
    // word at the last position in the returned array
    private static String[] add(String[] words, String word) {
        String[] bigger = new String[words.length + 1];
        for (int i = 0; i < words.length; i++) {
            bigger[i] = words[i];
        }
        bigger[bigger.length - 1] = word;
        return bigger;
    }
    ```

---
    # Enhanced for loop
    ``` Java
    private static int sum(int[] scores) {
        int sum = 0;
        for (int score : scores) {                // Equivalent
            sum += score;
        }
        return sum;
    }
    ```

--
    ```
    private static int sum(int[] scores) {
        int sum = 0;
        for (int i = 0; i < scores.length; i++) { // Equivalent
            int score = scores[i];                // Equivalent
            sum += score;
        }
        return sum;
    }
    ```