Notes

Outline

COM1100 Fundamentals of Computer Science –Winter 2000 Lecture 16 02/21/00

Reading this week Chapter 9 : Vectors and Arrays 9.7 Arrays Recitation handout 7 Individual project handout

Important dates 25th, Feb : recitation 7                  lab: individual project 3rd, March: recitation 8                  lab: array lab 6th, March : individual project due 10th, March: recitation 9                    lab: no new lab 16th, March: 8:00 Am Final Exam                       39 Snell Library

Lecture today Array How to declare an array How to initialize an array How to refer to individual elements in an array

Array Frequently, we may have a set of values (data), all of the same data type, that forms a logic group. One –dimensional array: a simple list containing individual items of the same data type The items in the list can be declared as a single unit and stored under a common variable name called the array name.

Array variable declaration Array variable declaration data_type  array_name[max_size]; Examples double temp[5]; // a floating-points array char codes[4]; // an character array int grades[6]; // an integer array

Array variable declaration Good programming practice requires the number of array items be defined as a constant before declaring the array. Thus, the previous array declaration would be declared using two statements, such as: const int NUMBER = 5; double temp[NUMBER]; const int ARRAYSIZE = 4;   char codes[ARRAYSIZE]; const int MAXSIZE = 6; int grades[MAXSIZE];

Individual elements in an array In these declaration statements, each array is allocated     sufficient memory to hold the number of data items given in the declaration statement. Each item in an array is called an element. The individual     elements are stored sequentially in the array.

How to access individual elements in an array? Any individual element can be accessed by giving the name of the array and the element’s position. This position is called the element’s index or subscript value. For a single-dimensional array, the first element has an index of 0 The index or subscript value gives the position of the element in the array. temp[0] is read as “ temp sub zero” temp[1] is read as “ temp sub 1”

How to access individual elements in an array? The subscript contained within brackets need not to be an constant integer Any expression that evaluates to an integer may be used as a subscripts. Examples: int i = 2; temp[i]; // the same as temp[2] temp[ i * 2]; // the same as temp[4]

Array bounds One cannot change the size of a given array Some C++ complier do not check the value of the indexing being used (called a bounds check) Compile time : no error messages Run time: crash or error Visual C++ complier does the bound check, but only give you some warning messages, not error messages. Example int temp[5]; // declare an integer array with 5 elements temp[2] = 5; // valid temp[5] = 3; // wrong, out of bound

Array initialization --1 Array can be declared and initialized at the same time. Examples int grades[6] = { 98, 87, 63, 74, 86, 76}; Size is 6 char codes[4] = { ‘F’, ‘S’, ‘C’, ’D’}; Size is 4 double temp[4] ={ 10.9, 54.8, 34.5, 42.1}; Size is 4

Array initialization --2 If the number of initializers is less than the declared number of elements listed in square brackets, the initializers are applied starting with array element 0. For example, int grades[4] = { 98, 87 }; grade[0] will be 98 grade[1] will be 87 The other array elements will be initialized to 0. grade[2] will be 0 grade[3] will be 0

Array initialization --3 A unique feature of initializers is that the size of an array may be omitted when initializing values are included in the declaration statement. And the actual size of the array will depend on how many elements in the { }. int grades[] = {98, 87, 63, 74, 86, 76}; Actual size will be 6 The complier will reserves enough storage space for 6 elements.

Character array initialization If I want to declare a character array and initialize it, there are normally three ways: char codes[6] = {‘s’, ’a’, ’m’, ’p’, ’l’, ’e’} Size is 6 char codes[]   = {‘s’, ’a’, ’m’, ’p’, ’l’, ’e’} Size is 6 char codes[] = “sample”; //no braces or commas Size is 7 We can use the string “sample” to initialize the codes array. This declaration created an array named codes having 7 elements. The last one is \0, also called null character. The null character is automatically appended to all strings by the C++ compiler.

Examples char codes[] ={'s','a','m','p','l','e'};    cout << codes[5] << endl; // valid    cout << codes[6] << endl; // warning C4700: local variable 'codes' used without // having been initialized // In other words, codes[6] is out of bound char codes1[] ="sample";    cout << codes1[5] << endl; // valid    cout << codes1[6] << endl; // valid