<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <meta name="author" content="Brandon Rozek"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta name="robots" content="noindex" /> <title>Brandon Rozek</title> <link rel="stylesheet" href="themes/bitsandpieces/styles/main.css" type="text/css" /> <link rel="stylesheet" href="themes/bitsandpieces/styles/highlightjs-github.css" type="text/css" /> </head> <body> <aside class="main-nav"> <nav> <ul> <li class="menuitem "> <a href="index.html%3Findex.html" data-shortcut=""> Home </a> </li> <li class="menuitem "> <a href="index.html%3Fcourses.html" data-shortcut=""> Courses </a> </li> <li class="menuitem "> <a href="index.html%3Flabaide.html" data-shortcut=""> Lab Aide </a> </li> <li class="menuitem "> <a href="index.html%3Fpresentations.html" data-shortcut=""> Presentations </a> </li> <li class="menuitem "> <a href="index.html%3Fresearch.html" data-shortcut=""> Research </a> </li> <li class="menuitem "> <a href="index.html%3Ftranscript.html" data-shortcut=""> Transcript </a> </li> </ul> </nav> </aside> <main class="main-content"> <article class="article"> <h1>Lecture Notes Oct 2nd</h1> <h2>Array</h2> <p><code>array</code> is not a reserved word, it's a concept. Arrays are able to hold multiple values under one name of the same type.</p> <p>For instance, you can have an array of integers.</p> <p>Properties of an array</p> <ul> <li>Size (n)</li> <li>index [0, n - 1]</li> </ul> <p>You can declare arrays by saying the type '[]' and the name of the array</p> <pre><code class="language-java">int[] numbers; double[] gpas; float[] grades;</code></pre> <p>Before you can use the array, you must <code>new</code> it</p> <pre><code class="language-java">numbers = new int[10];</code></pre> <p>Where 10 is the size of the array.</p> <p>You can combine both the declaration and initialization</p> <pre><code class="language-java">double[] points = new double[7];</code></pre> <p>You can access individual elements of the array by using its index. Indexes start from zero</p> <pre><code class="language-java">points[0] = 5.4; // The first element in the point array is 5.4</code></pre> <p>The <code>.length</code> property of an array gives the size of the array</p> <h2>For-Loops + Arrays</h2> <p>You can print out each element in the array using a for loop</p> <pre><code class="language-java">for (int i = 0; i < numbers.length; i++) { System.out.println(numbers[i]); }</code></pre> <p>You can ask a user to input a value to each element in the array</p> <pre><code class="language-java">for (int i = 0; i < points.length; i++) { System.out.print("Enter a number: "); points[i] = scnr.nextInt(); }</code></pre> <h2>While-Loops + Arrays</h2> <p>You can use a while loop to search the array</p> <pre><code class="language-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) }</code></pre> <p>If you don't include the <code>i != number.length</code> you will obtain an <code>IndexOutOfBounds</code> error.</p> <p>The example above is called a <em>Linear Search</em>. </p> <p>Linear searches work on an unsorted and sorted arrays.</p> <h2>Methods + Arrays</h2> <p>You can pass an array into a method</p> <pre><code class="language-java">public static void exampleMethod(int[] sample) { // Do something } public static void main(String[] args) { int[] s = new int[30]; exampleMethod(s); }</code></pre> <h2>Do-While Loops</h2> <p>For-loops can run 0 or more times. If you want something to execute at least once. Use a do-while loop.</p> <pre><code class="language-java">do { // Code } while (condition);</code></pre> <p>For example, to search at least once and asking whether the user wants to search again</p> <pre><code class="language-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');</code></pre> <p>You can create any type of loop just by using a while loop.</p> <h2>Example: Finding the Max</h2> <p>You can find the max of an array using the following method</p> <pre><code class="language-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);</code></pre> <h2>Example: Summing up an array</h2> <p>You can sum the array using the following method</p> <pre><code class="language-java">double sum = 0; for (int i = 0; i < arrayName.length; i++) { sum += arrayName[i]; } System.out.println("The sum is " + sum);</code></pre> </article> </main> <script src="themes/bitsandpieces/scripts/highlight.js"></script> <script src="themes/bitsandpieces/scripts/mousetrap.min.js"></script> <script type="text/x-mathjax-config"> MathJax.Hub.Config({ tex2jax: { inlineMath: [ ['$','$'], ["\\(","\\)"] ], processEscapes: true } }); </script> <script type="text/javascript" src="http://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"> </script> <script> hljs.initHighlightingOnLoad(); document.querySelectorAll('.menuitem a').forEach(function(el) { if (el.getAttribute('data-shortcut').length > 0) { Mousetrap.bind(el.getAttribute('data-shortcut'), function() { location.assign(el.getAttribute('href')); }); } }); </script> </body> </html>