Arrays. circleracers (one racer) Object Creation and "dot syntax" Array Operation Idiom. // the x-position of the racer float x = 0;

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1 Arrays Object Creation and "dot syntax" Array Operation Idiom CS Arrays 1 circleracers (one racer) // the x-position of the racer float x = 0; void draw() { background(245); // white drawracer(x, 40, 1); x += 1; // draw a racer at position x,y // draw the racer number void drawracer(float x, float y, int number) {... CS Arrays 2

2 circleracers (three racers) // the x-position of the racers float x1 = 0; float x2 = 0; float x3 = 0; void draw() { background(245); // white drawracer(x1, 40, 1); x1 += random(0, 3); drawracer(x2, 80, 2); x2 += random(0, 3); drawracer(x3, 120, 3); x3 += random(0, 3); CS Arrays 3 float x1 = 0; float x2 = 0; float x3 = 0; float x4 = 0; float x5 = 0; float x6 = 0; float x7 = 0; float x8 = 0; float x9 = 0; float x10 = 0; float x11 = 0; float x12 = 0; float x13 = 0; float x14 = 0; float x15 = 0; float x16 = 0; float x17 = 0; float x18 = 0; float x19 = 0; float x20 = 0; drawracer(x1, 40, i); x1 += random(0, 3); drawracer(x2, 80, i); x2 += random(0, 3); drawracer(x3, 120, i); x3 += random(0, 3); drawracer(x4, 160, i); x4 += random(0, 3); drawracer(x5, 200, i); x5 += random(0, 3); drawracer(x6, 240, i); x6 += random(0, 3); drawracer(x7, 280, i); x7 += random(0, 3); drawracer(x8, 320, i); x8 += random(0, 3); drawracer(x9, 360, i); x9 += random(0, 3); drawracer(x10, 400, i); x10 += random(0, 3); drawracer(x11, 440, i); x11 += random(0, 3); drawracer(x12, 480, i); x12 += random(0, 3); drawracer(x13, 520, i); x13 += random(0, 3); drawracer(x14, 560, i); x14 += random(0, 3); drawracer(x15, 600, i); x15 += random(0, 3); drawracer(x16, 640, i); x16 += random(0, 3); drawracer(x17, 680, i); x17 += random(0, 3); drawracer(x18, 720, i); x18 += random(0, 3); drawracer(x19, 760, i); x19 += random(0, 3); drawracer(x20, 800, i); x20 += random(0, 3);; CS Arrays 4

3 Array An array is a special variable that holds multiple values. Each value location is called an element. Each element is accessed using a unique index - The index is a whole number: 0, 1, 2, Variable a Array b[] b[0] b[1] b[2] b[3] b[4] CS Arrays 5 CS Arrays 6

4 Declaring an Array Array declare an array of ints int[] b; array of ints type array name Variable (for comparison) int a; int variable type variable name CS Arrays 7 Creating an Array new is an operator that means create we need to create the elements so they can hold values - normal variables have a single value, no need to create int[] b; create an array of 5 ints b = new int[5]; create type of values length of array CS Arrays 8

5 Declare and Create an Array in One Step int[] b = new int[5]; declare an array of ints called b create an array of 5 ints CS Arrays 9 Declare and Create Array Examples boolean[] boxstates; boxstates = new boolean[4]; float[] scores = new float[4]; int[] hues = new int[10]; int num = 5; float[] x = new float[num]; float[] y = new float[num]; boolean[] s = new boolean[num * 2]; CS Arrays 10

6 Valid or Invalid Array Declaration and Creation? int[] a = new int[2 * 10]; float[] b = new int[5]; boolean c = new boolean[5]; float[5] d; int[] e; e = new int[123]; float[] f = float[12]; int[] g = new int[1]; int[] h = new int[0]; CS Arrays 11 Assigning Values to an Array You assign values to each array element using the index int[] b = new int[5]; element index b[3] = 66; assign 66 to element at index 3 b[3] is the 4 th element CS Arrays 12

7 Initializing an Array Initializing an array is when you assign a value to each element after creating the array All elements are initialized to a default value when created - float and int are 0, boolean is false, String is null int[] b = new int[5]; initializing b[0] = 15; b[1] = 7; b[2] = -10; b[3] = 66; b[4] = 5; b[] b[0] b[1] b[2] b[3] b[4] CS Arrays 13 Creating and Initializing an Array in One Step create an array of 5 ints and initialize it to these values int[] b = {15, 7, -10, 66, 5; b[] b[0] b[1] b[2] b[3] b[4] CS Arrays 14

8 Using Arrays Use array elements just like variables int[] b = new int[5]; b[0] = 15; b[1] = random(-100, 100); println(b[2]); float c = b[0] * 100; b[3] = b[3] + 5; ellipse(b[0], b[1], b[2], b[2]); if (b[3] > 5) {... CS Arrays 15 You must create an array before using it if an array hasn't been created, it has no elements - trying to access an "uncreated array", is a runtime error: int[] b; b[0] = 666; // error b[4] = 678; // error b[]????? CS Arrays 16

9 Valid Index Values index must be between 0 and one less than array length - if array length is 5, index can be 0, 1, 2, 3, or 4 - otherwise, it's a runtime error: int[] b = new int[5]; b[-1] = 123; // error b[5] = 123; // error b[] b[0] b[1] b[2] b[3] b[4] CS Arrays 17 Valid Index Types an index must be an int type otherwise, it's a syntax error int[] b = new int[5]; b[1.0] = 15; // error float f = 2; b[f] = 7; // error b[] b[0] b[1] b[2] b[3] b[4] b[int(f)] = 7; // ok you can convert an int using int() CS Arrays 18

10 (error demos) int[] b = new int[5]; float f = 1; void setup() { println("start"); println(b[5]); // try -1, 1.0, f println("stop"); CS Arrays 19 What is printed to the console? int[] bar = new int[4]; void setup() { bar[0] = 5; bar[1] = 4; bar[2] = 3; bar[3] = 2; A. 1 B. 2 C. 3 D. 4 E. 5 println(bar[1]); CS Arrays 20

11 What is printed to the console? int[] bar = new int[5]; void setup() { bar[0] = 1; bar[1] = 2; bar[2] = 3; bar[3] = 4; bar[4] = bar[bar[1]]; A. 1 B. 2 C. 3 D. 4 E. 5 println(bar[4]); CS Arrays 21 circleracers (with array) // the x-position of the racers float[] x = new float[3]; void draw() { background(245); // white drawracer(x[0], 40, 1); x[0] += random(0, 3); drawracer(x[1], 80, 2); x[1] += random(0, 3); drawracer(x[2], 120, 3); x[2] += random(0, 3); CS Arrays 22

12 Variables for Indices Use variables or return values for indices int[] b = new int[5]; int i = 0; b[i] = 15; b[i + 1] = 7; b[int(random(0, 5))] = ; int() function converts to int, otherwise a syntax error CS Arrays 23 circleracers (with array) // the x-position of the racers float[] x = new float[3]; void draw() { background(245); // white int i = 0; drawracer(x[i], 40, i + 1); x[i] += random(0, 3); i++; drawracer(x[i], 80, i + 1); x[i] += random(0, 3); i++; drawracer(x[i], 120, i + 1); x[i] += random(0, 3); CS Arrays 24

13 circleracers (with array and loop) // the x-position of the racers float[] x = new float[3]; void draw() { background(245); // white int i = 0; while (i < 3) { // the y position is a "function of" i float y = (i + 1) * 40; drawracer(x[i], y, i + 1); x[i] += random(0, 3); i++; CS Arrays 25 How many Xs are printed to the console? for (int i = 0; i < 5; i++ ) { print("x"); A. 0 B. 1 C. 4 D. 5 E. 6 CS Arrays 26

14 What is printed to the console? int[] arr = new int[5]; for (int i = 0; i < 5; i++) { arr[i] = i; println(arr[4]); A. 0 B. 1 C. 4 D. 5 E. nothing, it s an error CS Arrays 27 Array Length Arrays know their own length - Arrays are objects - you access array length using object dot syntax int[] b = new int[5]; println(b.length); // prints 5 say b dot length b[b.length 1] = 123; // ok b[b.length] = 123; // error CS Arrays 28

15 circleracers (with array and loop) // the x-position of the racers float[] x = new float[5]; void draw() { background(245); // white int i = 0; while (i < x.length) { // the y position is a "function of" i float y = (i + 1) * 40; drawracer(x[i], y, i + 1); x[i] += random(0, 3); i++; CS Arrays 29 Array Operation Idiom Looping through an entire array to apply some operation to all elements is a common operation. // initialize array elements to same value for (int i = 0; i < myarray.length; i++) { myarray[i] = 50; // initialize array elements to random value for (int i = 0; i < myarray.length; i++) { myarray[i] = random(0, 100); CS Arrays 30

16 Array Operation: Sum all Elements Compute the total sum for all elements in an array by adding them one by one to an accumulator variable. // compute the sum of all elements float total = 0; for (int i = 0; i < myarray.length; i++) { total += myarray[i]; println("total:", total); CS Arrays 31 Array Operation: Average Element Value Sum all elements in an array and divide total by the length of the array to compute the average element size. // calculate the average value float total = 0; for (int i = 0; i < myarray.length; i++) { total += myarray[i]; float average = total / myarray.length; println("average:", average); CS Arrays 32

17 Array Operation: Find Largest Element Value Search the array to find the largest element value - Start by guessing that the largest element is the first one - check all other elements one-by-one to see if any are larger - if a larger one is found, use it as the largest element // find the largest element // (assuming myarray has at least 1 element) float largest = myarray[0]; for (int i = 1; i < myarray.length; i++) { if (myarray[i] > largest) { largest = myarray[i]; println("largest:", largest); CS Arrays 33 Array Operation: Find Largest Element Index Search the array to find the index with largest element value - Start by guessing that index 0 is the largest element index - check all other elements one-by-one to see if any are larger - if larger one is found, use it s index as the largest element index // find the index of the largest element // (assuming myarray has at least 1 element) int indexoflargest = 0; for (int i = 1; i < myarray.length; i++) { if (myarray[i] > myarray[indexoflargest]) { indexoflargest = i; println("index of largest:", indexoflargest); println("largest:", myarray[indexoflargest]); CS Arrays 34

18 Asymptotic Runtime of Algorithms O(1) and O(N) big Oh How many operations does it take to print one element? print(myarray[i]); How many operations does it take to add all elements? // compute the sum of all elements float total = 0; for (int i = 0; i < myarray.length; i++) { total += myarray[i]; println("total:", total); CS Arrays 35 Arrays as Function Parameters and Arguments float means a single floating point value float[] means an array of floating point values void func(float f) { void func(float[] a) { CS Arrays 36

19 largestvalue (in arrayoperations code) // return the largest element in array a // (assuming a has at least 1 element) float largestvalue(float[] a) { float largest = a[0]; for (int i = 1; i < a.length; i++) { if (a[i] > largest) { largest = a[i]; return largest; CS Arrays 37 arrayforest float[] treex = {166, 90, 77, 30, 110, 131, 55 ; float[] treeleafcolour = new float[treex.length]; void setup() {... // initialize to random tint of green for (int i = 0; i < treeleafcolour.length; i++ ) { treeleafcolour[i] = random(64, 130); void draw() {... // draw trees for forest for (int i = 0; i < treex.length; i++) { tree(treex[i], 95, treeleafcolour[i]); CS Arrays 38

20 EXTRA: Two Arrays, Shifting Elements in Array Textbook Example 9.6 CS Arrays 39 EXTRA: snake (LP Example 9-8) // Shift array values for (int i = 0; i < xpos.length - 1; i++) { xpos[i] = xpos[i + 1]; ypos[i] = ypos[i + 1]; // New location at end of array xpos[xpos.length - 1] = mousex; ypos[ypos.length - 1] = mousey; CS Arrays 40