Chapter 4. Section 4.5 Initialization of Arrays. CS 50 Hathairat Rattanasook

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1 Chapter 4 Section 4.5 Initialization of Arrays CS 50 Hathairat Rattanasook

2 One-Dimensional Arrays In an array, multiple values of the same data type can be stored with one variable name. Arrays can be used to store collections of related data Each element of an array has the same identification Each element has the same data type We can use the name of the variable to access all the elements in the collection An array s index starts from index 0 CS 50 - Hathairat Rattanasook 1

$Example: int test_scores[9] = {89, 78, 93, 68, 77, 83, 78, 65, 92}; // There is an array of nine elements. // Each element has type int.$

3 One-Dimensional Arrays cont. An array is different than other variables because an array can store multiple data. Every element in an array has the same data type. Example: int test_scores[9] = {89, 78, 93, 68, 77, 83, 78, 65, 92}; // There is an array of nine elements. // Each element has type int. CS 50 - Hathairat Rattanasook 2

4 One-Dimensional Arrays cont. The array properties int test_scores[9] = {89, 78, 93, 68, 77, 83, 78, 65, 92}; - The variable name: test_scores - The array length: 9 (a collection of nine data objects) - The indices of the array: the number, 0, 1,, 8 - Example of second element: test_scores[2] - The value of test_scores[2] is 93 CS 50 - Hathairat Rattanasook 3

5 Example: One-Dimensional Arrays cont. double doublearr[3] = { 1.1, 2.2, 3 }; The identifier of this array is doublearr It has the size 3 Every array index starts from 0. This array has indices 0, 1, and 2. Each element has type double Each element has the same identifier doublearr[0] is 1.1 doublearr[1] is 2.2 doublearr[2] is 3.0 *Though it seems like during the initialization the value is 3, the constant value 3 is automatically converted to the declaration type double. CS 50 - Hathairat Rattanasook 4

6 Three main things to know before using an array How to declare arrays How the individual cells are addressed How to initialize arrays CS 50 - Hathairat Rattanasook 5

7 An Array Declaration properties The type of elements that will be stored in the array The name of the array (identification) A pair of square bracket The number of cells in the array. A semicolon CS 50 - Hathairat Rattanasook 6

8 An Array Declaration An array type An array identification Size of an array CS 50 - Hathairat Rattanasook 7

9 Question? Which statement below is/are valid statement(s)? a. char name[6]; b. int numarray[5]; c. double 1doubleArray[3]; d. char name2[]; e. int numarray2[0]; f. double doublearray3[-2]; CS 50 - Hathairat Rattanasook 8

10 Answer Is your answer the same like my answer? a. char name[6]; valid b. int numarray[5]; valid c. double 1doubleArray[3]; invalid d. char name2[]; invalid e. int numarray2[0]; invalid f. double doublearray3[-2]; invalid invalid CS 50 - Hathairat Rattanasook 9

11 Do you know why they are invalid? invalid double 1doubleArray[3]; // an identifier cannot begin with a digit invalid char name2[]; // size of an array cannot be empty invalid int numarray2[0]; // an array must have at least one element invalid double doublearray3[-2]; //size of an array cannot be negative. CS 50 - Hathairat Rattanasook 10

12 The sizeof() an Array There is only one operator that can act on the array as a whole: the sizeof() operator. This operator indicates the total amount of memory used by the array. sizeof( example ); CS 50 - Hathairat Rattanasook 11

13 The sizeof() an Array cont. My machine (your machine may be different): an int occupies four bytes, char occupies one byte, and double occupies eight bytes. int intarr[5]; sizeof(intarr); // 4 x 5 = 20 intarr has 20 bytes char chararr[10]; sizeof(chararr); // 1 x 10 = 10 chararr has 10 bytes double doublearr[15]; sizeof(doublearr); // 8 x 15 = 120 doublearr has 120 bytes CS 50 - Hathairat Rattanasook 12

14 Question? What is the output of the following code? #include <stdio.h> #define MAX 5 int main() { float floatarray[max] = { 2.2, 3.3, 4.4 }; double num[3] = { 1, 2, 3.00 }; int i = 0; for (; i < 3; i++) { printf("\nnum is %lf", num[i]); } printf("\nsize of floatarray %d bytes", sizeof(floatarray)); printf("\nsize of num %d bytes", sizeof(num)); return 0; } CS 50 - Hathairat Rattanasook 13

15 Answer Recommend! Try it yourself ;) CS 50 - Hathairat Rattanasook 14

16 Chapter 4 Section 4.5 One-Dimensional Arrays CS 50 Hathairat Rattanasook CS 50 - Hathairat Rattanasook 15

17 Properties are Declaration of Arrays (again) 1) A basic data type 2) An identifier 3) A pair of square brackets 4) An int for the size of the array The size of an array must be larger than zero. *** Declaring an array without initialization MUST have the size of an array. 5) A semicolon to mark the end of the declaration statement CS 50 - Hathairat Rattanasook 16

18 Declaration an array example Once again! The size of an array must be provided during programming The size of an array must be a positive integer The size of an array cannot be changed during the run time An array can be any type CS 50 - Hathairat Rattanasook 17

19 Declaration and initialization an array at same time Properties are 1) A basic data type 2) A identifier 3) A pair of square brackets 4) An int for the size of the array 5) The size of an array must be larger than zero 6) An assignment operator 7) A pair of curly brackets 8) Constants or expressions must be separated by a comma 9) A semicolon CS 50 - Hathairat Rattanasook 18

20 Example CS 50 - Hathairat Rattanasook 19

21 Declaration and initialization an array at same time As you can see in the previous example, when declaring and initializing an array at the same time the size of the array is optional. float floatarray[] = { 2.2, 3.3, 4.4 }; The statement above is a valid statement. It is a float array of size 3. The compiler will automatically generate the size to this array. The intarray has the size 6. int intarray[] = { 1,2,3,4,5,6}; CS 50 - Hathairat Rattanasook 20

22 Question? Which statement(s) is/are a valid declaration and initialization of an array at the same time? char a[5] = { 'A', 'B', 'C', 'D', 'E', '\0' }; int b[5] = { 'A', 'B', 'C' } int c[5] = { 1, 2, 3, 4, 5 }; float d[] = { 2.2, 3.3, 4.4 }; double e[3] = { 1, 2, 3.00 }; int f[5] = { 1, 2, 3.00}; CS 50 - Hathairat Rattanasook 21

23 invalid valid valid valid valid invalid Answer char a[5] = { 'A', 'B', 'C', 'D', 'E', '\0' }; // The array has size 5 but initialized with 6 values int b[5] = { 'A', 'B', 'C' } // It is ok to be assigned the value only some elements // A character in C is also type int int c[5] = { 1, 2, 3, 4, 5 }; // The array c has size 5 and it is assigned values to all five elements float d[] = { 2.2, 3.3, 4.4 }; // A compiler will automatically generate the size to the array d which is 3 double e[3] = { 1, 2, 3.00 }; // The first and the second element will automatically converted into type double. int f[5] = { 1, 2, 3.00}; // The array is declared as type int. It cannot have an element of type float or double CS 50 - Hathairat Rattanasook 22

24 How to access an element of an array? A chararray of six elements Access each element by using an index chararray[0]; // the first element chararray[1]; // the second element chararray[2]; // the third element CS 50 - Hathairat Rattanasook 23

25 Question? Can you use a for-loop to access each element of an array below? #include <stdio.h> #define MAX 5 int main() { } int intarray[max] = {1,2,3,4,5}; // implement your code here return 0; CS 50 - Hathairat Rattanasook 24

26 Answer Of course! I can do it. #include <stdio.h> #define MAX 5 int main() { int intarray[max] = { 1,2,3,4,5 }; int index; // my code is here for (index = 0; index < MAX; index++) { printf("\nindex is %d : intarray is %d", index,intarray[index]); } return 0; } CS 50 - Hathairat Rattanasook 25

Today. o main function. o cout object. o Allocate space for data to be used in the program. o The data can be changed

Today. o main function. o cout object. o Allocate space for data to be used in the program. o The data can be changed CS 150 Introduction to Computer Science I Data Types Today Last we covered o main function o cout object o How data that is used by a program can be declared and stored Today we will o Investigate the