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content/ta/fall2017/cpsc220/oct2.md

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+# Lecture Notes Oct 2nd
+
+## Array
+
+`array` is not a reserved word, it's a concept. Arrays are able to hold multiple values under one name of the same type.
+
+For instance, you can have an array of integers.
+
+Properties of an array
+
+- Size (n)
+- index [0, n - 1]
+
+You can declare arrays by saying the type '[]' and the name of the array
+
+```java
+int[] numbers;
+double[] gpas;
+float[] grades;
+```
+
+Before you can use the array, you must `new` it
+
+```java
+numbers = new int[10];
+```
+
+Where 10 is the size of the array.
+
+You can combine both the declaration and initialization
+
+```java
+double[] points = new double[7];
+```
+
+You can access individual elements of the array by using its index. Indexes start from zero
+
+```java
+points[0] = 5.4; // The first element in the point array is 5.4
+```
+
+The `.length` property of an array gives the size of the array
+
+## For-Loops + Arrays
+
+You can print out each element in the array using a for loop
+
+```java
+for (int i = 0; i < numbers.length; i++) {
+    System.out.println(numbers[i]);
+}
+```
+
+You can ask a user to input a value to each element in the array
+
+```java
+for (int i = 0; i < points.length; i++) {
+    System.out.print("Enter a number: ");
+    points[i] = scnr.nextInt();
+}
+```
+
+## While-Loops + Arrays
+
+You can use a while loop to search the array
+
+```java
+int i = 0;
+int number = 5;
+// While the index is within the array size and the number isn't found
+while (i != number.length && number != numbers[i]) {
+    i++
+}
+if (i == numbers.length) {
+    System.out.println(number + " was not found.")
+} else {
+    System.out.println(number + " was found at index " + i)
+}
+```
+
+If you don't include the `i != number.length` you will obtain an `IndexOutOfBounds` error.
+
+The example above is called a *Linear Search*. 
+
+Linear searches work on an unsorted and sorted arrays.
+
+
+
+## Methods + Arrays
+
+You can pass an array into a method
+
+```java
+public static void exampleMethod(int[] sample) {
+    // Do something
+}
+public static void main(String[] args) {
+    int[] s = new int[30];
+    exampleMethod(s);
+}
+```
+
+
+
+## Do-While Loops
+
+For-loops can run 0 or more times. If you want something to execute at least once. Use a do-while loop.
+
+```java
+do {
+    // Code
+} while (condition);
+```
+
+For example, to search at least once and asking whether the user wants to search again
+
+```java
+// Assume linearSearch and array are defined
+char answer;
+Scanner input = new Scanner(System.in);
+do { 
+  linearSearch(array, input);
+  System.out.print("Do you want to search again? (Y/N) ");
+  input.nextLine();
+  answer = input.next().charAt(0);
+} while( answer != 'N');
+```
+
+You can create any type of loop just by using a while loop.
+
+
+
+## Example: Finding the Max
+
+You can find the max of an array using the following method
+
+```java
+double max = arrayName[0];
+for (int i = 1; i < arrayName.length; i++) {
+    if (max < arrayName[i]) {
+        max = arrayName[i];
+    }
+}
+System.out.println("The max is " + max);
+```
+
+
+
+## Example: Summing up an array
+
+You can sum the array using the following method
+
+```java
+double sum = 0;
+for (int i = 0; i < arrayName.length; i++) {
+    sum += arrayName[i];
+}
+System.out.println("The sum is " + sum);
+```
+