1. Chapter 8 Arrays Dr. Jiung-yao Huang Dept. Comm. Eng.
Nat. Chung Cheng Univ.
TA: 鄭筱親 陳昱豪

2. 本章重點
Declaring and referencing arrays
When the array name with no subscript, it represents an address, the address of the initial array element (陣列與指標的曖昧關係)
const

3. Outline 8.1 DECLARING AND REFERENCING ARRAYS 8.2 ARRAY SUBCRIPTS
8.3 USING FOR LOOPS FOR SEQUENTIAL ACCESS
8.4 USING ARRAY ELEMENTS AS FUNCTION ARGUMENTS
8.5 ARRAY ARGUMENTS
8.6 SEARCHING AND SORTING AN ARRAY
8.7 MULTIDIMENSIONAL ARRAYS
8.8 ARRAY PROCESSING ILLUSTRATED
CASE STUDY:
ANALYSIS OF SALES DATA
8.9 COMMON PROGRAMMING ERRORS

4. 8.1 DECLARING AND REFERENCING ARRAYS
To group data items together is more efficient and comprehensible
Data structure
A composite of related data items stored under the same name
Array
A collection of data items of the same type
Array element
A data item that is part of an array
Subscripted variable
A variable followed by a subscript in brackets, designating an array element
Array subscript
A value or expression enclosed in brackets after the array name, specifying which array element to access

5. Figure 8.1 The Eight Elements of Array x

6. PARALLEL ARRAYS
Two or more arrays with the same number of elements used for storing related information about a collection of data objects
5503
4556
5691 …
9146
id [0]
id [1]
id [2]
id [49]
2.71
3.09
2.98 …
1.92
gpa [0]
gpa [1]
gpa [2]
gpa [49]

7. EXAMPLE 8.3 #define NUM_QUEST 10 #define NUM_CLASS_DAYS 5 typedef enum
{monday, tuesday, wednesday, thursday, friday}
class_days_t;
char answer [NUM_QUEST];
int score [NUM_CLASS_DAYS];

8. Figure 8.2 Arrays answer and score

9. ARRAY INITIALIZATION
Initialize a 25-elements array with the prime numbers less than 100
int prime_lt_100 [ ] = {2, 3, 5, 7, 11, 13, 17, , 23, 29, 31, 37, , 43, 47, 53, 59, , 67, 71, 73, 79, , 89, 97}

10. ARRAY DECLARATION SYNTAX: EXAMPLE: element-type aname [size];
#define A_SIZE 5
double a[A_SIZE];
char vowels [ ] = {‘A’, ‘E’, ‘I’, ‘O’, ‘U’};

11. printf(“%d”,prime[i]); /*result is 3*/
8.2 ARRAY SUBCRIPTS
SYNTAX:
aname [subscript]
EXAMPLE:
int prime[] = {2, 3, 5, 7} , i = 1;
printf(“%d”,prime[i]); /*result is 3*/

12. 8.3 USING FOR LOOPS FOR SEQUENTIAL ACCESS
Use an indexed for loop, a counting loop whose loop control variable runs from zero to one less than the array size.
Use the loop counter as an array index (subscript) gives access to each array element in turn.

13. The name SIZE has been defined to be 11.
EXAMPLE 8.7
The array square will be used to store the squares of the integers 0 through 10.
The name SIZE has been defined to be 11.
int square[SIZE], i;
for (i=0;i<SIZE;++i)
square [i]= i * i;
[0]
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10] 1 4 9 16 25 36 49 64 81
100

14. STATISTICAL COMPUTATIONS USING ARRAYS
One common use of arrays is for storage of a collection of related data values.
Once the values are stored, we can perform some simple statistical computations.
Figure 8.3 first for loop
for (i=0; i<MAX_ITEM; ++i);
scanf(“%lf”, &x[i]);

15. Figure 8.3 Program to Print a Table of Differences

16. Figure 8.3 Program to Print a Table of Differences (cont’d)

17. 8.4 USING ARRAY ELEMENTS AS FUNCTION ARGUMENTS
EXAMPLE 8.9:
The function prototype below shows one type double input parameter(arg_1) and two double * output parameters(arg2_p and arg3_p).
Figure 8.4
void do_it (double arg_1, double *arg2_P, double *arg3_p);
do_it (p, &q, &r);
do_it (x[0], &x[1], &x[2]);

18. Figure 8.4 Data Area for Calling Module and Function do_it

19. Formal array parameters
8.5 ARRAY ARGUMENTS
Formal array parameters
When an array name with no subscript appears in the argument list of a function call, the address of the initial array element is actually stored in the function’s corresponding formal parameter.
The function manipulates the original array, not its own personal copy, so an assignment changes the original array

20. EXAMPLE 8.10
The statement list[i]=in_value stores in_value in element i of its actual array argument
In function fill_array, the array parameter is declared as int list[ ]
The argument declaration does not indicate the size of list.
Since we do not provide the size, we have the flexibility to pass to the function an array of any number of integers.

21. Figure 8.5 Function fill_array

22. ARGUMENT CORRESPONDENCE FOR ARRAY PARAMETERS
fill_array(y, 10, num)
store the value num in the ten elements of array y
fill_array(x, 5, 1)
store 1 in five elements of array x
Because C stores the address of the type int variable x[0] in list, the call of fill_array
fill_array(&x[0], 5, 1)
execute exactly like the call above

23. Figure 8.6 Data Areas Before Return from fill_array (x, 5, 1);

24. USE OF *list INSTEAD OF list[ ] IN A FORMAL PARAMETER LIST
Use either parameter declaration
int list[ ]
int *list
The first tells us that the actual argument is an array.
The second declaration would be equally valid for an integer array parameter.

25. Use list as an array input parameter.
EXAMPLE 8.11
Function get_max in Fig. 8.7 can be called to find the largest value in an array.
Use list as an array input parameter.
If x is a five-element array of type int values, the statement
x_large = get_max(x,5)
used to search for largest element

26. Figure 8.7 Function to Find the Largest Element in an Array

27. ARRAY AS INPUT ARGUMENTS
ANSI C provides a qualifier in the declaration of the array formal parameter in order to notify the C compiler that the array is only an input to the function and that the function does not intend to modify the array.
const

28. ARRAY INPUT PARAMETER SYNTAX: EXAMPLE:
const element-type array-name [ ]
const element-type *array-name
EXAMPLE:
int get_min_sub(const double data[ ], int data_size) {
int i, small_sub;
small_sub=0;
for (i=1; i<data_size; ++i)
if (data[i] < data[small_sub])
small_sub=i;
return(small_sub); }

29. Figure 8.8 Diagram of a Function That Computes an Array Result
In C, it is not legal for a function’s return type to be an array.

30. n specifies how many corresponding elements are summed.
EXAMPLE 8.12
The sum of arrays ar1 and ar2 is defined as arsum such that arsum[i] is equal to ar1[i] + ar2[i] for each subscript i.
n specifies how many corresponding elements are summed.
The formal parameter list declaration
const double ar1[ ]
const double ar2[ ]
double arsum[ ]
int n

31. Figure 8.9 Function to Add Two Arrays

32. Figure 8.10 Function Data Areas for add_arrays(x, y, x_plus_y, 5);

33. x_plus_y after call to add_arrays
We assume that a calling function has declared three five-element arrays x, y, and x_plus_y and has filled x and y with data.
The call
add_arrays(x, y, x_plus_y, 5)
lead to
&
Not used
x_plus_y after call to add_arrays
3.5
6.7
4.7
9.1
12.2

34. PARTIALLY FILLED ARRAYS
In order to reuse an array for processing more than one data set, the programmer declares an array large enough to hold the largest data set anticipated.

35. EXAMPLE 8.13
The purpose of function fill_to_sentinel is to fill a type double array with data until the designated sentinel value is encountered in the input data. (Figure 8.11)

36. Figure 8.11 Diagram of Function fill_to_sentinel

37. Figure 8.12 Function Using a Sentinel-Controlled Loop to Store Input Data in an Array

38. Figure 8.13 Driver for Testing fill_to_sentinel

39. STACKS Stack pop push 應用
A data structure in which only the top element can be accessed.
pop
Remove the top element of a stack
push
Insert a new element at the top of the stack 應用
老鼠走迷宮，算式計算，呼叫副程式，改遞迴

40. push(s, ‘2’, &s_stop, STACK_SIZE); push(s, ‘+’, &s_stop, STACK_SIZE);
EXAMPLE
char s[STACK_SIZE];
Int s_stop = -1;
push(s, ‘2’, &s_stop, STACK_SIZE);
push(s, ‘+’, &s_stop, STACK_SIZE);
push(s, ‘C’, &s_stop, STACK_SIZE); C + 2

41. Figure 8.14 Functions push and pop

42. Figure 8.14 Functions push and pop (cont’d)

43. 8.6 SEARCHING AND SORTING AN ARRAY
Array search
In order to search an array, we need to know the search target.
The search loop should be exited when the target value is found that the process is called a linear search.

44. ALGORITHM 1. Assume the target has not been found.
2. Start with the initial array element.
3. Repeat while the target is not found and there are more array elements
4. if the current element matches the target
5. Set a flag to indicate that the target has been found
else
6. Advance to the next array element
7. if the target was found
8. Return the target index as the search result
9.Return -1 as the search result

45. Figure 8.15 Function That Searches for a Target Value in an Array

46. SORTING AN ARRAY ALGORITHM FOR SELECTING SORT
for each value of fill from 0 to n-2
2. Find index_of_min, the index of the smallest in the unsorted subarray list[fill] through list[n-1]
3. if fill is not the position of the smallest element (index_of_min)
4. Exchange the smallest with the one at position fill

47. Figure 8.16 Trace of Selection Sort

48. Figure 8.17 Function select_sort

49. 8.7 MULTIDIMENSIONAL ARRAYS
An array with two or more dimensions
A two-dimensional object that many are familiar with is a tic-tac-toe board.
The array declaration
char tictac[3][3];

50. Figure 8.18 A Tic-tac-toe Board Stored as Array tictac

51. Multidimensional Array Declaration
SYNTAX:
element-type aname [size1] [size2] …[sizen]
element-type aname [ ] [size2] …[sizen] // prototype
EXAMPLES:
double table [NROWS][NCOLS];
void process_matrix(int in[ ][4], int out[ ][4], int nrows)

52. Initialization of Multidimensional Arrays
You can initialize multidimensional arrays in their declarations just like you initialize one-dimensional arrays.
Instead of listing all table values in one list, the values are usually grouped by rows.
Example:
char array[2][2] = { { 'a‘ , ‘b'}, {‘c', ‘d'} };

53. EXAMPLE 8.15
Function filled checks whether a tic-tac-toe board is completely filled.
If board contains no cells with the value ‘ ‘ , the function returns 1 for true; otherwise, it returns 0 for false.

54. Figure 8.19 Function to Check Whether Tic-tac-toe Board Is Filled

55. ARRAYS WITH SEVERAL DIMENSIONS
The array enroll declared
int enroll [MAXCRS][5][4]
course
campus
year
year
campus
course

56. Figure 8.20 Three-Dimensional Array enroll

57. 8.8 ARRAY PROCESSING ILLUSTRATED CASE STUDY：Analysis of Sales Data(1/4) (自修)
Step 1: Problem
The sales manager of your company needs a sales analysis program to track sales performance by salesperson and by quarter.
The program will read all sales transactions from a text file.
The data for each transaction will be the salesperson’s number, the quarter in which the sale took place, and the sales amount.
The sales transactions are in no particular order.
After scanning all sales transactions, the program should display a table in the form shown in Fig. 8.21, which totals by person and by quarter.

58. Figure 8.21 Sales Analysis Output

59. CASE STUDY：Analysis of Sales Data(2/4)
Step 2: Analysis
Data requirements
New type
quarter_t {fall, winter, spring, summer}
Problem constants
NUM_SALES_PEOPLE 5
NUM_QUARTERS
Problem inputs
Sales transaction file
double sales [NUM_SALES_PEOPLE][NUM_QUARTERS]
Problem outputs
double person_totals [NUM_SALES_PEOPLE]
double quarter_totals [NUM_QUARTERS]

60. CASE STUDY：Analysis of Sales Data(3/4)
Step 3: Design
Initial algorithm
1.Scan sales data, posting by salesperson and quarter, and returning a value to show success or failure of the data scan.
2.if the data scan proceeded without error
3. Compute salesperson totals (row sums)
4. Compute quarterly totals (column sums)
5. Display the sales table along with the row
and column sums

61. CASE STUDY：Analysis of Sales Data(4/4)
Step 4: Implementation (Figure 8.22、Figure 8.23)
Step 5: Testing

62. Figure 8.22 Sales Analysis Main Function

63. Figure 8.23 Function scan_table and Helper Function initialize

64. Figure 8.23 Function scan_table and Helper Function initialize (cont’d)

65. Figure 8.23 Function scan_table and Helper Function initialize (cont’d)

66. Figure 8.24 Function display_table and Helper Function display_quarter

67. Figure 8.24 Function display_table and Helper Function display_quarter (cont’d)

68. Common Programming Errors (1/4)
The most common error in using arrays is a subscript-range error.
Ecample:
int array[10];
array[10] = 10; /*the value is */
/* from 0 to 9 */

69. Common Programming Errors (2/4)
If a subscript-range error occurs inside an indexed loop, verify that the subscript is in range for both the initial and the final values of the loop control variable.
Example:
int array[5], i;
for ( i = 1; i <= 5; i++) /*range is 0 to 4*/
…..

70. Common Programming Errors (3/4)
Not to apply the address-of operator to the array name even if the array is an output argument.
Example:
int array[5];
go(&array); /*Wrong using*/

71. Common Programming Errors (4/4)
Use the correct forms for declaring array input and output parameters in function prototypes.
Example:
int *z
/*It could represent a single integer output*/
/*parameter or an integer array parameter.*/
int z[ ]

72. Chapter Review(1/2)
An array is a data structure used to store a collection of data items of the same type.
An individual array element is referenced by replacing immediately after the array name a square-bracketed subscript for each dimension.
The initial element of a one-dimensional array x is referenced as x[0]. If x has n elements, the final element is referenced as x[n-1].

73. Chapter Review(2/2)
For an array declared as a local variable, space is allocated in the function data area for all the array elements.
For an array declared as a function parameter, space is allocated in the function data area for only the address of the initial element of the actual argument passed.
The name of an array with no subscript always refers to the address of the initial array element.
A function that creates an array result should require the calling module to pass an output argument array in which to store the result.

74. Question?

75. 宣告時, 只有兩種情況可以少填第一個維度, 其他均要填[ ] 內的值
Array 的宣告跟使用
宣告時, 只有兩種情況可以少填第一個維度, 其他均要填[ ] 內的值
未配置空間，僅作定義用
Formal parameters
int getmax(int n, int list[])
External variables
extern int a[];
Initialization 可得知第一個維度的個數時
使用時, 均要填[ ]內的值