Arrays. Array Data Type. Array - Memory Layout. Array Terminology. Gaddis: 7.1-3,5

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1 Arrays Unit 5 Gaddis: 7.1-3,5 CS 1428 Spring 2018 Ji Seaman Array Data Type Array: a variabe that contains mutipe vaues of the same type. Vaues are stored consecutivey in memory. An array variabe decaration statement in C++: int numbers[5]; This creates an array caed numbers which contains 5 integer vaues (ints). 1 2 Array - Memory Layout The definition: int numbers[5]; aocates the foowing memory: (vaues are stored consecutivey in memory) first eement second eement third eement fourth eement fifth eement Array Terminoogy Given the foowing array definition: int numbers[5]; numbers is the name of the array int is the data type of the array eements 5 is the size decarator: the number of eements (vaues) in the array. 3 4

2 Size Decarator 7.2 Accessing Array Eements The size decarator must be an integer and a constant. it must be greater than 0 IT CANNOT BE A VARIABLE!* It can be a itera or a named constant. const int SIZE = 40; doube grades[size]; Named constants ease program maintenance when the size of the array must be changed. *Uness you are using a specia compier (mine is not specia). 5 Each eement of the array has a unique subscript (or index) that indicates its position in the array. The subscripts are 0-based the first eement has subscript 0 the second eement has subscript 1... the ast eement has subscript (size -1) the ast eement s subscript is n-1 where n is the number of eements in the array 6 Accessing Array Eements Given this array decaration: int numbers[5]; The syntax to access one eement is: numbers[2] //the third eement of numbers array Pronounced numbers at 2 or numbers sub 2 Array subscripts The subscript is ALWAYS an integer regardess of the type of the array eements. the subscript can be ANY integer expression itera: 2 numbers[2] variabe: i numbers[i] expression: (i+2)/2 numbers[(i+2)/2] 7 8

3 Inputting array contents Most array operations must be done one eement at a time. Input programming assignment grades for a student in CS1428: << programming assignment scores: << end; cin >> scores[0]; cin >> scores[1]; cin >> scores[2]; cin >> scores[3]; cin >> scores[4]; cin >> scores[5]; cin >> scores[6]; Is there a better way? 9 Array input using a oop We can use a for oop to input into the array The subscript/index can be the oop variabe: << programming assignment scores: << end; i starts at 0, the first vaid subscript oop ends when i is 7, the first invaid subscript This code is equivaent to the code on the 10 previous side. Array output using a oop We can aso use a for oop to output the eements of the array: << programming assignment scores: << end; cout << You entered these vaues: ; cout << scores[i] << ; cout << end; 11 Array initiaization You can initiaize arrays when they are defined. const int NUM_SCORES = 3; foat scores[num_scores] = {86.5, 92.1, 77.5; Vaues are assigned in order: scores[0] = 86.5 scores[1] = 92.1 scores[2] = NOTE: uninitiaized arrays have GARBAGE vaues stored in them (not necessariy 0). 12

4 Partia Array Initiaization When you initiaize, you don t need to specify a vaue for every position. foat scores[7] = {86.5, 92.1, 77.5; Impicit array sizing When you initiaize, you don t need to specify the size decarator. foat scores[] = {86.5, 92.1, 77.5; In this case, the first 3 eements are initiaized to the specified vaues. The uninitiaized vaues WILL be set to 0!!!! In this case, the compier determines the size of the array from the number of eements isted C++: No bounds checking C++ does not check it to make sure an array subscript is vaid (between 0 and size-1) If you use a subscript that is outside the bounds of the array you may not get a warning or error. You may unintentionay change memory aocated to other variabes. const int SIZE = 3; int vaues[size]; for (int i=0; i < 5; i++) { vaues[i] = 100; This code defines a threeeement array and then writes five vaues to it (changing the memory after the array) Processing Array Contents Given the foowing array definition: doube tests[10]; the expression tests[i] may be used exacty ike any variabe of type doube. tests[0] = 79; cout << tests[0]; cin >> tests[1]; tests[4] = tests[0] + tests[1]; 16

5 Using array eements: doube vaues[3]; //array definition vaues[0] = 22.3; //assignment to array eement vaues[1] = 11.1; cout << Enter a number: ; cin >> vaues[2]; doube sum = vaues[0] + vaues[1] + vaues[2]; doube avg = sum/3.0; cout << Vaues at zero: << vaues[0] << end; int i=2; if (vaues[i] > 32.0) cout << Above freezing << end; 17 Operations over Entire Arrays Generay there are NO operations that you can perform over an entire array. Some operations may appear to work (no errors) but you don t get the desired resuts. int numbers1[] = {1, 2, 3; int numbers2[] = {4, 5, 6; cin >> numbers1; //input, won t work cout << numbers1 << end; //output, won t work numbers1 = numbers2; //assignment, won t work if (numbers1==numbers2) //comparison, won t work... numbers3 = numbers1 + numbers2; //addition, won t work 18 Summing vaues in an array We can use a for oop to sum the eements of the array (the running tota) << programming assignment scores: << end; int tota = 0; //initiaize accumuator tota = tota + scores[i]; How do you get the average programming assignment score? 19 Finding the maximum vaue in an array We can use a for oop to find the max vaue: Note: keep track of the maximum vaue encountered so far (the running maximum) << programming assignment scores: << end; int maximum = scores[0]; //init max to first eem for (int i=1; i < NUM_SCORES; i++) { //start i at 1 if (scores[i] > maximum) maximum = scores[i]; //save the new maximum 20 // no ese needed

6 Array assignment To copy/assign one array to another, you must assign eement by eement. const int SIZE = 4; int vaues1[size] = {100, 200, 300, 400; int vaues2[size]; // vaues2 = vaues1; WRONG, won t work correcty for (int i = 0; i < SIZE; i++) { vaues2[i] = vaues1[i]; Note: this aso does not work: vaues2 = {3,6,9,27; //ony works for initiaization 21