Week 7 - Friday

 What did we talk about last time?  Array examples  Sound

 We can represent a deck of cards as an array of 52 items  One easy way is to make each item a String giving the name of the card  We can extend last time's lab and store each of these names in an array

 Swapping the values of two variables is a fundamental operation in programming  It is going to become more important in arrays because now the order of variables has become important  The simplest way to swap two variables involves using a third variable as a temporary location

 Here is an example of swapping two String s indexed i and j in an array of String s called array int i = in.nextInt(); int j = in.nextInt(); String temp = array[i]; array[i] = array[j]; array[j] = temp; int i = in.nextInt(); int j = in.nextInt(); String temp = array[i]; array[i] = array[j]; array[j] = temp;

 Using the swap code, we can do a random shuffling of a deck  To do so, we go through each element of the array, and randomly swap it with any of the later elements for( int i = 0; i < n; i++ ) { exchange = i + (int)(Math.random() * (n - i)); temp = deck[i]; deck[i] = deck[exchange]; deck[exchange] = temp; } for( int i = 0; i < n; i++ ) { exchange = i + (int)(Math.random() * (n - i)); temp = deck[i]; deck[i] = deck[exchange]; deck[exchange] = temp; }

 Audio data on Windows machines is sometimes stored in a WAV file  A WAV file is much simpler than an MP3 because it has no compression  Even so, it contains two channels (for stereo) and can have many different sample rates and formats for recording sound  The StdAudio class lets you read and write a WAV file easily and always deal with a single array of sound, sampled at 44,100 Hz

 Everything you’d want to do with sound:  To do interesting things, you have to manipulate the array of samples  Make sure you added StdAudio.java to your project before trying to use it MethodUse double[] read(String file) Read a WAV file into an array of double s void save(String file, double[] input) Save an array of double s (samples) into a WAV file void play(String file) Play a WAV file void play(double[] input) Play an array of double s (samples)

 Let’s load a file into an array:  If the song has these samples:  Perhaps samples will contain: String file = "song.wav"; double[] samples = StdAudio.read(file); String file = "song.wav"; double[] samples = StdAudio.read(file);

 With the audio samples loaded into the array named samples, we can play them as follows: StdAudio.play(samples);

 Or, we could generate sound from scratch with StdAudio  This example from the book creates 1 second of the pitch A440: double[] sound = new double[StdAudio.SAMPLE_RATE + 1]; for( int i = 0; i < sound.length; i++ ) sound[i] = Math.sin(2 * Math.PI * i * 440 / StdAudio.SAMPLE_RATE); StdAudio.play(sound); double[] sound = new double[StdAudio.SAMPLE_RATE + 1]; for( int i = 0; i < sound.length; i++ ) sound[i] = Math.sin(2 * Math.PI * i * 440 / StdAudio.SAMPLE_RATE); StdAudio.play(sound);

 What if we wanted to play the second half of a sound followed by the first half?  I know, why would we want to do that? double[] samples = StdAudio.read(file); double[] switched = new double[samples.length]; for(int i = 0; i < samples.length/2; i++ ) switched[i + samples.length/2] = samples[i]; for(int i = samples.length/2; i < samples.length; i++ ) switched[i - samples.length/2] = samples[i]; StdAudio.play(switched); double[] samples = StdAudio.read(file); double[] switched = new double[samples.length]; for(int i = 0; i < samples.length/2; i++ ) switched[i + samples.length/2] = samples[i]; for(int i = samples.length/2; i < samples.length; i++ ) switched[i - samples.length/2] = samples[i]; StdAudio.play(switched);

 StdDraw

 Keep reading Chapter 6 of the textbook  Read Project 3 carefully and get started  It's a harder project than the previous two!  Office hours from 3:30-5pm canceled this today due to travel