An Introduction to Programming with C Sixth Edition

An Introduction to Programming with C++ Sixth Edition Chapter 12 Two-Dimensional Arrays

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 An Introduction to Programming with C++, Sixth Edition 2

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 An Introduction to Programming with C++, Sixth Edition 3

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. An Introduction to Programming with C++, Sixth Edition 4

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 An Introduction to Programming with C++, Sixth Edition 5

Figure 12 -1 Names of some of the variables in the two-dimensional orders array An Introduction to Programming with C++, Sixth Edition 6

Using Two-Dimensional Arrays (cont’d. ) Figure 12 -2 Problem specification for the Caldwell Company’s orders program An Introduction to Programming with C++, Sixth Edition 7

Figure 12 -2 IPO chart for the Caldwell Company’s orders program An Introduction to Programming with C++, Sixth Edition 8

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: data. Type array. Name [number. Of. Rows] [number. Of. Columns] = {{initial. Values}, {initial. Values }, …{initial. Values }}; • data. Type specifies the data type of elements in the array (all elements must have same data type) • number. Of. Rows and number. Of. Columns specify number of rows and columns in array, respectively An Introduction to Programming with C++, Sixth Edition 9

Declaring and Initializing a Two. Dimensional Array (cont’d. ) • You initialize elements in a two-dimensional array by entering a separate initial. Values section, enclosed in braces, for each row of the array • Maximum number of initial. Values sections you may enter is the number of rows in the array • Within individual initial. Values 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 An Introduction to Programming with C++, Sixth Edition 10

Figure 12 -3 How to declare and initialize a two-dimensional array An Introduction to Programming with C++, Sixth Edition 11

Declaring and Initializing a Two. Dimensional Array (cont’d. ) Figure 12 -4 Illustration of the two-dimensional grades array An Introduction to Programming with C++, Sixth Edition 12

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: array. Name [row. Subscript] [column. Subscript ] = expression; – expression can include any combination of constants, variables, and operators • Must match data type of array An Introduction to Programming with C++, Sixth Edition 13

Entering Data into a Two-Dimensional Array (cont’d. ) • Syntax for extraction operator: cin >> array. Name [row. Subscript][column. Subscript ]; An Introduction to Programming with C++, Sixth Edition 14

Figure 12 -5 How to use an assignment statement to assign data to a two-dimensional array An Introduction to Programming with C++, Sixth Edition 15

Figure 12 -5 How to use an assignment statement to assign data to a two-dimensional array (cont’d. ) An Introduction to Programming with C++, Sixth Edition 16

Figure 12 -6 How to use the extraction operator to store data in a two-dimensional array An Introduction to Programming with C++, Sixth Edition 17

Figure 12 -6 How to use the extraction operator to store data in a two-dimensional array (cont’d. ) An Introduction to Programming with C++, Sixth Edition 18

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 An Introduction to Programming with C++, Sixth Edition 19

Figure 12 -7 How to display the contents of a two-dimensional array An Introduction to Programming with C++, Sixth Edition 20

Figure 12 -7 How to display the contents of a two-dimensional array (cont’d. ) An Introduction to Programming with C++, Sixth Edition 21

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 An Introduction to Programming with C++, Sixth Edition 22

Coding the Caldwell Company’s Orders Program Figure 12 -8 IPO chart information and C++ instructions for the Caldwell Company’s orders program An Introduction to Programming with C++, Sixth Edition 23

Figure 12 -8 IPO chart information and C++ instructions for the Caldwell Company’s orders program (cont’d. ) An Introduction to Programming with C++, Sixth Edition 24

Figure 12 -9 The Caldwell Company’s orders program An Introduction to Programming with C++, Sixth Edition 25

Figure 12 -10 Sample run of the Caldwell Company’s orders program An Introduction to Programming with C++, Sixth Edition 26

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 An Introduction to Programming with C++, Sixth Edition 27

Figure 12 -11 Problem specification, IPO chart information, and C++ instructions for the Jenko Booksellers program An Introduction to Programming with C++, Sixth Edition 28

Accumulating the Value Stored in a Two-Dimensional Array (cont’d. ) Figure 12 -11 Problem specification, IPO chart information, and C++ instructions for the Jenko Booksellers program (cont’d. ) An Introduction to Programming with C++, Sixth Edition 29

Figure 12 -12 The Jenko Booksellers program An Introduction to Programming with C++, Sixth Edition 30

Accumulating the Value Stored in a Two-Dimensional Array (cont’d. ) Figure 12 -13 Result of running the Jenko Booksellers program An Introduction to Programming with C++, Sixth Edition 31

Searching a Two-Dimensional Array • Program for the Wilson Company uses a four-row, 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 An Introduction to Programming with C++, Sixth Edition 32

Figure 12 -14 Problem specification, IPO chart information, and C++ instructions for the Wilson Company program An Introduction to Programming with C++, Sixth Edition 33

Figure 12 -14 Problem specification, IPO chart information, and C++ instructions for the Wilson Company program (cont’d. ) An Introduction to Programming with C++, Sixth Edition 34

Figure 12 -14 Problem specification, IPO chart information, and C++ instructions for the Wilson Company program (cont’d. ) An Introduction to Programming with C++, Sixth Edition 35

Figure 12 -15 Sample run of the Wilson Company program Figure 12 -16 Another sample run of the Wilson Company program An Introduction to Programming with C++, Sixth Edition 36

Figure 12 -17 Wilson Company program An Introduction to Programming with C++, Sixth Edition 37

Figure 12 -17 Wilson Company program (cont’d. ) An Introduction to Programming with C++, Sixth Edition 38

Searching a Two-Dimensional Array (cont’d. ) Figure 12 -18 Desk-check table after the statements on lines 11 through 21 are processed An Introduction to Programming with C++, Sixth Edition 39

Searching a Two-Dimensional Array (cont’d. ) Figure 12 -19 Desk-check table after the nested loop is processed the first time An Introduction to Programming with C++, Sixth Edition 40

Searching a Two-Dimensional Array (cont’d. ) Figure 12 -20 Desk-check table after the nested loop is processed the second time An Introduction to Programming with C++, Sixth Edition 41

Searching a Two-Dimensional Array (cont’d. ) Figure 12 -21 Desk-check table after the nested loop ends during the second search An Introduction to Programming with C++, Sixth Edition 42

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) An Introduction to Programming with C++, Sixth Edition 43

Figure 12 -22 Modified Caldwell Company’s orders program An Introduction to Programming with C++, Sixth Edition 44

Figure 12 -22 Modified Caldwell Company’s orders program (cont’d. ) An Introduction to Programming with C++, Sixth Edition 45

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 twodimensional 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 An Introduction to Programming with C++, Sixth Edition 46

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 An Introduction to Programming with C++, Sixth Edition 47

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 An Introduction to Programming with C++, Sixth Edition 48

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 An Introduction to Programming with C++, Sixth Edition 49

Lab 12 -1: Stop and Analyze • Study the program in Figure 12 -23 and then answer the questions • The company array contains the amounts the company sold both domestically and internationally during the months January through June – The first row contains the domestic sales for the three months – The second row contains the international sales during the same period An Introduction to Programming with C++, Sixth Edition 50

Lab 12 -2: Plan and Create • Plan and create a program for Falcon Incorporated • Program should display a shipping charge based on number of items ordered (entered by user) Figure 12 -24 Problem specification for Lab 12 -2 An Introduction to Programming with C++, Sixth Edition 51

Lab 12 -3: Modify • Modify the program in Lab 12 -2 • Replace the maximum amounts in the ship. Charges array with the minimum amounts • Make the appropriate modifications to the program • Run and test the program appropriately An Introduction to Programming with C++, Sixth Edition 52

Lab 12 -4: Desk-Check • Desk-check the Jenko Booksellers program in Figure 12 -12 An Introduction to Programming with C++, Sixth Edition 53

Lab 12 -5: Debug • Open the program in the Lab 12 -5. cpp file • Debug the program An Introduction to Programming with C++, Sixth Edition 54