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Chapter 8 Arrays Dr. Jiung-yao Huang Dept. Comm. Eng. Nat. Chung Cheng Univ. E-mail : [email protected] TA: 鄭鄭鄭 鄭鄭鄭

Chapter 8 Arrays Dr. Jiung-yao Huang Dept. Comm. Eng. Nat. Chung Cheng Univ. E-mail : [email protected] TA: 鄭筱親 陳昱豪

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Chapter 8Arrays

Dr. Jiung-yao HuangDept. Comm. Eng.Nat. Chung Cheng Univ.E-mail : [email protected]: 鄭筱親 陳昱豪

3-2中正大學通訊工程系 潘仁義老師 Advanced Network Technology Lab

本章重點

Declaring and referencing arraysWhen 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

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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

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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

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Figure 8.1 The Eight Elements of Array x

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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]

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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];

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Figure 8.2 Arrays answer and score

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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, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97}

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ARRAY DECLARATION

SYNTAX: element-type aname [size];

EXAMPLE: #define A_SIZE 5

double a[A_SIZE];

char vowels [ ] = {‘A’, ‘E’, ‘I’, ‘O’, ‘U’};

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8.2 ARRAY SUBCRIPTS

SYNTAX: aname [subscript]

EXAMPLE:

int prime[] = {2, 3, 5, 7} , i = 1;

printf(“%d”,prime[i]); /*result is 3*/

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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.

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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 4 9 16 25 36 49 64 81 100

[0] [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

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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 loopfor (i=0; i<MAX_ITEM; ++i);

scanf(“%lf”, &x[i]);

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Figure 8.3 Program to Print a Table of Differences

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

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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 8.4void do_it (double arg_1, double *arg2_P, double *arg3_p);do_it (p, &q, &r);do_it (x[0], &x[1], &x[2]);

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Figure 8.4 Data Area for Calling Module and Function do_it

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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

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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.

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Figure 8.5  Function fill_array

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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

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

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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.

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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

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Figure 8.7 Function to Find the Largest Element in an Array

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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

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ARRAY INPUT PARAMETER

SYNTAX: 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);}

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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.

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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

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Figure 8.9 Function to Add Two Arrays

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

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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

3.5 6.7 4.7 9.1 12.2

x_plus_y after call to add_arrays

& Not used

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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.

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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)

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Figure 8.11 Diagram of Function fill_to_sentinel

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

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Figure 8.13 Driver for Testing fill_to_sentinel

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STACKS

Stack A data structure in which only the top element

can be accessed.pop

Remove the top element of a stackpush

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

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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

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Figure 8.14 Functions push and pop

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Figure 8.14 Functions push and pop (cont’d)

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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.

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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 elements4. 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 element7. if the target was found

8. Return the target index as the search result else

9.Return -1 as the search result

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

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SORTING AN ARRAYALGORITHM FOR SELECTING SORT

1. 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

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Figure 8.16 Trace of Selection Sort

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Figure 8.17 Function select_sort

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8.7 MULTIDIMENSIONAL ARRAYS

Multidimensional array 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];

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

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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)

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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'} };

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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.

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

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ARRAYS WITH SEVERAL DIMENSIONS

The array enroll declared int enroll [MAXCRS][5][4]

course campus year

year campus

course

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Figure 8.20 Three-Dimensional Array enroll

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8.8 ARRAY PROCESSING ILLUSTRATEDCASE 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.

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Figure 8.21 Sales Analysis Output

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CASE STUDY : Analysis of Sales Data(2/4)

Step 2: AnalysisData requirements

New typequarter_t {fall, winter, spring, summer}

Problem constantsNUM_SALES_PEOPLE 5NUM_QUARTERS 4

Problem inputsSales transaction filedouble sales [NUM_SALES_PEOPLE][NUM_QUARTERS]

Problem outputsdouble person_totals [NUM_SALES_PEOPLE]double quarter_totals [NUM_QUARTERS]

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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

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CASE STUDY : Analysis of Sales Data(4/4)

Step 4: Implementation (Figure 8.22 、 Figure 8.23)

Step 5: Testing

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Figure 8.22 Sales Analysis Main Function

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Figure 8.23 Function scan_table and Helper Function initialize

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

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

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Figure 8.24 Function display_table and Helper Function display_quarter

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

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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 */

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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*/

…..

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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*/

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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[ ]

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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].

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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.

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Question?

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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 variablesextern int a[];

Initialization 可得知第一個維度的個數時使用時 , 均要填 [ ]內的值