Chapter 12 Two-Dimensional Arrays

Transcription

1 Chapter 12 Two-Dimensional Arrays

2 Objectives Declare and initialize a two-dimensional array Enter data into a two-dimensional array Display the contents of a two-dimensional array Sum the values in a two-dimensional array Search a two-dimensional array Pass a two-dimensional array to a function 2

3 Using Two-Dimensional Arrays Recall that an array is a group of related variables that have the same data type You can visualize a one-dimensional array as a column of variables in memory You can visualize a two-dimensional array as a table in that the variables are in rows and columns You can determine the number of variables in a two-dimensional array by multiplying the number of rows by the number of columns 3

4 Using Two-Dimensional Arrays (cont d.) Each variable in a two-dimensional array is identified by a unique combination of two subscripts specifying the variable s row and column position Variables located in the first, second, etc. row of a two-dimensional array are assigned a row subscript of 0, 1, etc. Similarly, variables located in the first, second, etc. column of a two-dimensional array are assigned a column subscript of 0, 1, etc. 4

5 Using Two-Dimensional Arrays (cont d.) You refer to each variable in a two-dimensional array by the array s name immediately followed by the variable s row and column subscripts (in that order), each enclosed in its own set of square brackets As with one-dimensional arrays, the last row and column subscripts of a two-dimensional array will always be one less than the number of rows and columns (respectively) in the array, since the subscripts begin at 0 5

6 Declaring and Initializing a Two- Dimensional Array You must declare a two-dimensional array before you use it As with one-dimensional arrays, it is good practice to initialize the array variables Syntax for declaring a two-dimensional array: datatype arrayname [numberofrows] [numberofcolumns] = {{initialvalues}, {initialvalues }, {initialvalues }}; datatype specifies the data type of elements in the array (all elements must have same data type) numberofrows and numberofcolumns specify number of rows and columns in array, respectively 6

7 Declaring and Initializing a Two- Dimensional Array (cont d.) You initialize elements in a two-dimensional array by entering a separate initialvalues section, enclosed in braces, for each row of the array Maximum number of initialvalues sections you may enter is the number of rows in the array Within individual initialvalues sections, you enter one or more values separated by commas Maximum number of values you may enter in a row is the number of columns 7

8 How to declare and initialize a two-dimensional array 8

9 Declaring and Initializing a Two- Dimensional Array (cont d.) Illustration of the two-dimensional grades array 9

10 Entering Data into a Two-Dimensional Array You can use either an assignment statement or the extraction operator to enter data into the elements of a two-dimensional array Syntax for assignment statement: arrayname [rowsubscript] [columnsubscript ] = expression; expression can include any combination of constants, variables, and operators Must match data type of array 10

11 Entering Data into a Two-Dimensional Array (cont d.) Syntax for extraction operator: cin >> arrayname [rowsubscript][columnsubscript ]; 11

12 How to use an assignment statement to assign data to a two-dimensional array 12

13 How to use an assignment statement to assign data to a two-dimensional array (cont d.) 13

14 How to use the extraction operator to store data in a two-dimensional array 14

15 How to use the extraction operator to store data in a two-dimensional array (cont d.) 15

16 Displaying the Contents of a Two- Dimensional Array To display the contents of a two-dimensional array, you must access its individual elements You can use two counter-controlled loops One to keep track of the row subscript One to keep track of the column subscript 16

17 How to display the contents of a two-dimensional array 17

18 How to display the contents of a two-dimensional array (cont d.) 18

19 Coding the Caldwell Company s Orders Program Program that uses a two-dimensional array to store the number of orders received from each of the Caldwell Company s four sales regions during the first three months of the year Each row in the array represents a region, and each column represents a month Program allows the user to enter the order amounts and then displays the amounts on the computer screen 19

20 Coding the Caldwell Company s Orders Program IPO chart information and C++ instructions for the Caldwell Company s orders program 20

21 IPO chart information and C++ instructions for the Caldwell Company s orders program (cont d.) An Introduction to Programming with C++, Sixth Edition 21

22 The Caldwell Company s orders program 22

23 Sample run of the Caldwell Company s orders program 23

24 Accumulating the Values Stored in a Two-Dimensional Array Program for the Jenko Booksellers company uses a two-dimensional array to store the sales made in each of the company s three bookstores Array contains three rows and two columns First column contains sales amount for paperback books sold in each of three stores Second column contains sales amounts for hardcover books in the three stores Program calculates total sales by accumulating amounts stored in array and displays total sales 24

25 Problem specification, IPO chart information, and C++ instructions for the Jenko Booksellers program 25

26 Accumulating the Value Stored in a Two-Dimensional Array (cont d.) Problem specification, IPO chart information, and C++ instructions for the Jenko Booksellers program (cont d.) 26

27 The Jenko Booksellers program 27

28 Accumulating the Value Stored in a Two-Dimensional Array (cont d.) Result of running the Jenko Booksellers program 28

29 Searching a Two-Dimensional Array Program for the Wilson Company uses a fourrow, two-column array to store the company s four pay codes and their corresponding pay rates Pay codes are stored in first column of each row Pay rate associated with each code is stored in the same row as its pay code, in the second column Program gets a pay code from user and searches for pay code in the array s first column If pay code is found, corresponding pay rate is displayed; otherwise, Invalid pay code is displayed 29

30 Problem specification, IPO chart information, and C++ instructions for the Wilson Company program 30

31 Problem specification, IPO chart information, and C++ instructions for the Wilson Company program (cont d.) 31

32 Problem specification, IPO chart information, and C++ instructions for the Wilson Company program (cont d.) 32

33 Figure Sample run of the Wilson Company program Another sample run of the Wilson Company program 33

34 Wilson Company program 34

35 Wilson Company program (cont d.) 35

36 Searching a Two-Dimensional Array (cont d.) Desk-check table after the statements on lines 11 through 21 are processed 36

37 Searching a Two-Dimensional Array (cont d.) Desk-check table after the nested loop is processed the first time 37

38 Searching a Two-Dimensional Array (cont d.) Desk-check table after the nested loop is processed the second time 38

39 Searching a Two-Dimensional Array (cont d.) Desk-check table after the nested loop ends during the second search 39

40 Passing a Two-Dimensional Array to a Function Like one-dimensional arrays, two-dimensional arrays are passed automatically by reference When passing a two-dimensional array to a function, function header and prototype should contain formal parameter consisting of name of array followed by two sets of square brackets containing the number of rows and columns, respectively Number of rows is not required (first set of brackets may be left empty) 40

41 Modified Caldwell Company s orders program 41

42 Modified Caldwell Company s orders program (cont d.) 42

43 Summary A two-dimensional array resembles a table in that elements are in rows and columns Each element has the same data type You can determine the number of elements in a two-dimensional array by multiplying the number of rows by the number of columns Each element in a two-dimensional array is identified by a unique combination of two subscripts representing the element s row and column, respectively 43

44 Summary (cont d.) You refer to each element in a two-dimensional array by the array s name immediately followed by the element s subscripts in two sets of square brackets First row and column subscripts in a twodimensional array are 0 Last row and column subscripts are always one number less than the number of rows and columns, respectively You must declare a two-dimensional array before you can use it 44

45 Summary (cont d.) When declaring a two-dimensional array, you must provide the number of rows as well as the number of columns You can use an assignment statement or the extraction operator to enter data into an array You need to use two loops to access every element in a two-dimensional array One of the loops keeps track of the row subscript, and the other keeps track of the column subscript 45

46 Summary (cont d.) To pass a two-dimensional array to a function, you include the array s name in the statement that calls the function Array s corresponding formal parameter in the function header must specify the formal parameter s data type and name, followed by two sets of square brackets First bracket contains the number of rows, and the second bracket contains the number of columns 46