Review break and continue while if break while

Review: break and continue . . while (…) {. . . if (…) break; . . . } while (…) {. . . if (…) continue; . . . } . . .

Probability Machine

Arrays § array: A variable that stores many values of the same type. index 0 1 2 3 4 5 6 7 8 9 value 12 49 -2 26 5 17 -6 84 72 3 element 0 element 4 element 9 § element: One value in an array. § index: A 0 -based integer used to access an element from an array.

Declaring an array: int[] numbers = new int[10]; index 0 1 2 3 4 5 6 7 8 9 value 0 0 0 0 0 General Syntax: type[] name = new type[size]; The array's length can be any expression. int len = scnr. next. Int(); int[] data = new int[len];

Array auto-initialization When arrays are initially constructed, every element is automatically initialized to the "zero" value for that type. int: 0 double: 0. 0 boolean: false char: '' ← the "null character" String or object: null ← means "no object" index 0 1 2 3 4 value 0 0 0 index 0 1 2 3 An array of doubles value 0. 0 An array of integers

Assigning a value to an array element: numbers[0] = 27; numbers[3] = -6; index 0 value 27 1 2 3 4 5 6 7 8 9 0 0 -6 0 0 0 General Syntax array. Name[index] = expression; numbers[i] = 4; numbers[i+1] = 5*6;

Using an array element's value in an expression: array. Name[index] System. out. println(numbers[0]); if (numbers[3] < 0) { System. out. println("Element 3 is negative"); } index 0 value 27 1 2 3 4 5 6 7 8 9 0 0 -6 0 0 0

Out-of-bounds indexes § The indexes that are legal to access in an array are those in the range of 0 to the array's length - 1. § Reading or writing any index outside this range will throw an Array. Index. Out. Of. Bounds. Exception. § Example: int[] data = new int[10]; System. out. println(data[0]); System. out. println(data[-1]); System. out. println(data[9]); System. out. println(data[10]); // // okay exception index 0 1 2 3 4 5 6 7 8 9 value 0 0 0 0 0

Arrays of other types § Example: double[] results = new double[6]; results[2] = 3. 4; results[5] = -0. 5; index 0 1 2 3 4 5 value 0. 0 3. 4 0. 0 -0. 5 § Example: boolean[] tests = new boolean[6]; tests[3] = true; index 0 1 2 3 4 5 value false true false

Activity: What are the final contents of the array? int[] numbers = new int[8]; numbers[1] = 4; numbers[4] = 99; numbers[7] = 2; int x = numbers[1]; numbers[x] = 44; numbers[7]] = 11; 0 numbers 1 2 3 4 5 6 7

Arrays and for loops § Arrays are very commonly used with for loops that pass over each element and process it in some way: § Example (print each element of an array): for (int i = 0; i < 8; i++) { System. out. print(numbers[i] + " "); } System. out. println(); § Output: 0 4 11 0 44 0 0 2

§ Example: assigning each array element a value in a for loop. for (int i = 0; i < 8; i++) { numbers[i] = i * i; } index 0 1 2 3 4 5 6 7 value 0 1 4 9 16 25 36 49

Initializing Arrays § Often we need to put preset values into an array. § Java provides a way to quickly initialize an array: int[] days. In. Month = {31, 28, 31, 30, 31}; § General syntax: type[] name = {value, … value}; § This syntax is useful when you know in advance what the array's contents will be. § You don't explicitly specify the array's size. § The Java compiler figures out the size by looking at the number of values. String[] days. Names = {"Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"};

Activity: § What are the final values stored in the array? int[] a = {2, 5, 1, 6, 14, 7, 9}; for (int i = 1; i < a. length; i++) { a[i] += a[i - 1]; }

Example: Using an array to count letters: § Goal count the frequency of each letter in a string, and then print all the non-zero counts. § Example: Mississippi I: M: P: S: 4 1 2 4

Counting the letters using an array of counts A B C D E F G H I J K L 0 1 2 3 4 5 6 7 8 9 10 11 3 1 20 0 0 12 0 0 0 10 2 ALFALFA

// count and print all letters occurring in the string // only prints for those letters that occur at least once public static void count. All. Letters(String s) { int[] counts = new int[26]; // counts for A to Z s = s. to. Upper. Case(); // count all the letters for (int i = 0; i < s. length(); i++) { char c = s. char. At(i); if (Character. is. Letter(c)) { int index = c - 'A'; counts[index]++; } } } // print the non-zero counts for (int index = 0; index < 26; index++) { if (counts[index] > 0) System. out. println((char)('A'+index) + ": " + counts[index]); }

War. And. Peace. txt A: B: C: D: E: F: G: H: I: J: K: L: M: 204435 34377 60663 117757 313034 54507 50915 166519 172645 2488 20285 96041 61282 N: O: P: Q: R: S: T: U: V: W: X: Y: Z: 183136 191506 44724 2319 146901 162132 224524 64922 26787 58931 4032 45940 2386

show code using arrays in probabalility machine