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1 C++ FOR ENGINEERS AND SCIENTISTS THIRD EDITION Chapter 7 Arrays

2 Objectives 2 In this chapter, you will learn about: One-dimensional arrays 一維陣列 Array initialization 陣列起始化 Declaring and processing two-dimensional arrays 二維陣列 Arrays as arguments 陣列作為引數 Statistical analysis 統計分析

3 Objectives (continued) 3 The Standard Template Library (STL) 標準模板庫 Searching and sorting 搜尋和排序 Common programming errors 常見錯誤

4 4 7.1 one-dimensional arrays 一維陣列

5 One-Dimensional Arrays 一維陣列 5 One-dimensional array: A list of related values with the same data type, stored using a single group name (called the array name) 相同類型的相關資料用共通名字儲存 ( 陣列名稱 ) Syntax: datatype arrayname[number-of-items] By convention, the number of items is first declared as a constant, and the constant is used in the array declaration 一般習慣先將陣列大小宣告為常數, 再宣告陣列

6 One-Dimensional Arrays (continued) 6 Examples: const int NUMELS = 6; int volts[numels]; const int ARRAYSIZE = 4; char code[arraysize]; Figure 7.1 The volts and code arrays in memory

One-Dimensional Arrays (continued) 7 Element: An item in the array 陣列元素 Array storage of elements is contiguous 陣列中的元素是連續儲存的 Index (or subscript) of an element: The position of the element

7 One-Dimensional Arrays (continued) 7 Element: An item in the array 陣列元素 Array storage of elements is contiguous 陣列中的元素是連續儲存的 Index (or subscript) of an element: The position of the element within the array 指標或下標 : 元素在陣列中的位置 Indexes are zero relative 從 0 起算 To reference an element, use the array name and the index of the element 用陣列名稱和指標來指定元素 Figure 7.2 Identifying array elements

8 One-Dimensional Arrays (continued) 8 Index represents the offset from the start of the array 下標代表從陣列開頭的差值 Element is also called indexed variable or subscripted variable 元素又稱為指標變數或下標變數 Subscripted variable can be used anywhere that a variable can be used 陣列元素可以用在任何變數可用的地方 Expressions can be used within the brackets if the value of the expression 方括號中也可用運算式 Yields an integer value 但是結果需整數 Is within the valid range of subscripts 在下標的有效範圍內

9 One-Dimensional Arrays (continued) 9 All of the elements of an array can be processed by using a loop 陣列元素可以用迴圈來處理 The loop counter is used as the array index to specify the element 迴圈指標用為陣列指標 Example: sum = 0; for (i=0; i<5; i++) sum = sum + temp[i];

10 Input and Output of Array Values 10 陣列值的輸入和輸出 Array elements can be assigned values interactively using a cin stream object 可以用 cin 互動輸入 Out of range array indexes are not checked at compile time 編譯時並不會檢查指標是否超出範圍 May produce run time errors 可能產生執行錯誤 May overwrite a value in the referenced memory location and cause other errors 可能覆寫其他變數 Array elements can be displayed using the cout stream object 陣列元素可以使用 cout 顯示

11 Input and Output of Array Values (continued) 11 用迴圈輸入一系列溫度用迴圈輸出一系列溫度

12 Input and Output of Array Values (continued) 12 用迴圈輸入一系列溫度把溫度加總

13 array initialization 陣列起始化

14 Array Initialization 陣列起始化 14 Array elements can be initialized in the array declaration statement 可以在宣告時起始 Example: int temp[5] = {98, 87, 92, 79, 85}; Initialization: Can span multiple lines, because white space is ignored in C++ 可以跨越多行, 空格多寡不受影響 Starts with array element 0 if an insufficient number of values is specified 從陣列元素 0 開始 ( 即使提供的數值不夠多 ) If initializing in the declaration, the size may be omitted 如果宣告時起始化, 可以不寫陣列大小

15 Array Initialization (continued) 15 char array will contain an extra null character at the end of the string 字串陣列會在結尾加一個空字元 Example: char codes[] = sample ; Figure 7.4 Initializing a character array with a string adds a terminating \0 character

16 Array Initialization (continued) 16 找出一系列數字中的最大值

17 declaring and processing twodimensional arrays 二維陣列

18 Declaring and Processing Two-Dimensional Arrays 宣告和處理二維陣列 18 Two-dimensional array: Has both rows and columns 二維陣列有列欄 Also called a table 也叫做表格 Both dimensions must be specified in the array declaration 宣告時指定兩個維數的大小 Row is specified first, then column 先 row 再 column Both dimensions must be specified when referencing an array element 指定元素時需要同時指定兩個維數

19 Declaring and Processing 19 Two-Dimensional Arrays (continued) Example: int val[1][3]; Figure 7.5 Each array element is identified by its row and column position

20 Declaring and Processing 20 Two-Dimensional Arrays (continued) Two-dimensional arrays can be initialized in the declaration by listing values within braces, separated by commas 起始化二維陣列時將數字放在大括號 {} 中, 以逗點隔開 Braces can be used to distinguish rows, but are not required 大括號可以用來分辨 rows, 但是不是必要

21 Declaring and Processing 21 Two-Dimensional Arrays (continued) Nested for loops are used to process twodimensional arrays 使用巢狀 for 迴圈處理二維陣列 Outer loop controls the rows 外面迴圈控制橫列 Inner loop controls the columns 內側迴圈控制欄位

22 Declaring and Processing Two-Dimensional Arrays (continued) 22 處理二維陣列將每個數字乘以 10

23 Larger Dimensional Arrays 更高維 23 陣列 Arrays with more than two dimensions can be created, but are not commonly used 二維以上陣列罕見 Think of a three-dimensional array as a book of data tables Figure 7.7 Representation of a three-dimensional array

24 arrays as arguments 陣列作為引數

25 Arrays as Arguments 陣列作為引數 25 An individual array element can be passed as an argument just like any individual variable 單一陣列元素可以當做一個獨立變數傳給函數 The called function receives a copy of the array element s value 被呼叫的函數接收該陣列元素的一個複製版本 Passing an entire array to a function causes the function to receive a reference to the array, not a copy of its element values 但是傳送整個陣列時是提供陣列的地址, 不是複製的值 The function must be declared with an array as the argument 函數必須宣告一個陣列為引數 Single element of array is obtained by adding an offset to the array s starting location 從陣列的起始位址可以推算出其他元素的位址

26 Arrays as Arguments (continued) 26 宣告陣列指相同的陣列只是名稱不同 Figure 7.8 Only one array is created 只有產生一個陣列

27 Arrays as Arguments (continued) 27 將陣列起始位址傳給函數 Figure 7.9 The array s starting address is passed

28 Program 7.7

29 Arrays as Arguments (continued) 29 Figure 7.10 Storage of the val array 可以推算出其他元素的位址

30 A Case Study: Statistical Analysis 30 Create a program that: Accepts a list of 10 grades as input Calculates the average and standard deviation Displays the results of the calculations

31 Program 7.10

32 Program 7.10 (continued)

33 Common Programming Errors 33 Failing to declare the array 宣告陣列錯誤 Using a subscript that references a non-existent array element (out of bounds) 參照不存在的陣列元素 Failing to use a counter value in a loop that is large enough to cycle through all array elements 控制便數值不夠大, 不能用到所有陣列元素 Failing to initialize the array 陣列起始錯誤

34 Summary 34 Single dimension array is a data structure that stores a list of values having the same data type 一維陣列是儲存一系列相同資料型態數值的資料結構 Array elements are stored in contiguous memory locations, and referenced by array name and index position 陣列元素儲存在連續的記憶體位置, 使用陣列名稱和指標來參照 Two-dimensional array has rows and columns 二維陣列有列和欄 Arrays may be initialized when they are declared 陣列可以在宣告時起始化

35 Summary (continued) 35 Arrays may be passed to a function by passing the name of the array as the argument 陣列可以傳送給函數 Individual array elements as arguments are passed by value 單一陣列元素使用數值傳送 Arrays passed as arguments are passed by reference, not by value 整個陣列是用記憶體位置傳送

Fun Time (1) What happens in memory? 1 i n t i ; 2 s h o r t j ; 3 double k ; 4 char c = a ; 5 i = 3; j = 2; 6 k = i j ; H.-T. Lin (NTU CSIE) Referenc

References (Section 5.2) Hsuan-Tien Lin Deptartment of CSIE, NTU OOP Class, March 15-16, 2010 H.-T. Lin (NTU CSIE) References OOP 03/15-16/2010 0 / 22 Fun Time (1) What happens in memory? 1 i n t i ; 2