A First Book of ANSI C - Chiang Mai University · A First Book of ANSI C, Fourth Edition 3 Chapter...

A First Book of ANSI CFourth Edition

Chapter 8

Arrays

A First Book of ANSI C, Fourth Edition 2

Objectives

• One-Dimensional Arrays

• Array Initialization

• Arrays as Function Arguments

• Case Study: Computing Averages and

Standard Deviations

• Two-Dimensional Arrays

• Common Programming and Compiler

Errors


Chapter 8 Arrays

• The variables used so far, scalar variables,each variable can only be used to store a single value at a time or atomic type.

• This means that the value cannot be further

subdivided or separated into a legitimate

data type

• Frequently we may have a set of values, all

of the same data type, or called a single-

dimensional array, that form a logical group.


8.1 One Dimensional Arrays

• A one-dimensional array is a list of values of

the same data type.

int grades[5] ;

More Examples

• char code[4] ; // an array of four character codes

• double prices[6] ; // an array of six double precision prices

• float amount [100] ; //an array of 100 floating point amounts


Examples using the elements of the grades array are

grades [0] = 98 ;

grades [1] = grades [0] – 11

grades [2] = 2 * ( grades [0] – 6 );

grades [3] = 79 ;

grades [4] = (grades [2] + grades [3] – 3 ) / 2 ;

total = grades [0] + grades [1] + grades [2] + grades [3] + grades [4] ;

How to use for loop for adding five grade values?

One extremely important advantage of using integer expressions as subscripts

is that it allows sequencing through an array using a for loop.


Find maximum value

• When an element with a higher value is

located, that element becomes the new

maximum.

maximum = price[0];

for (i = 1; i <= 999; i++)

if (price[i] > maximum)

maximum = price[i];


Input and Output of Array Values

• Individual array elements can be assigned

values using individual assignment

statements or, interactively , using the

scanf( ) function.

Examples of individual data entry statements are

price[5] = 10.69 ;

scanf (“%d %lf”, &grades[0] , &price[2] );

scanf (“%c”, &code[0] );

scanf (“%d %d %d”, &grades[0], &grades[1], &grades[2]);


• Alternatively, a for statement can be used to cycle through the array for interactive data input.

For example , the code

for (i = 0 ; i <= 4 ; ++i )

{

printf (“Enter a grade : ”);

scanf (“%d”, &grade[i] );

}

• prompts the user for five grades .

• The first grade entered is stored in grades[0] , the second in grades[1] , and so on until all five grades are entered .


• One caution should be mentioned about

storing data in an array.

• C does not check the value of the index

being used.

• If an array has been declared as consisting

of 10 elements, for example, and you use an

index of 12, which is outside the bounds of

the array, C will not notify you of the error

when the program is compiled.


• During output , individual array elements can

be displayed using the printf( ) function or

complete sections of the array can be

displayed by including a printf( ) function call

within a for loop .

• Examples of this are

printf (“%lf ,” price[6] );

printf (“The value of element %d is %d”, i , grades[i] );

for ( n = 5 ; n <= 20 ; ++n )

printf (“%d %lf”, n , price[n] );


Sample output:Enter a grade: 85

Enter a grade: 90

Enter a grade: 78

Enter a grade: 75

Enter a grade: 92

grades 0 is 85

grades 1 is 90

grades 2 is 78

grades 3 is 75

grades 4 is 92

Example of Input and Output of Array Values


Statement is outside of the second for loop; total

is displayed only once, after all values have been

added

Example of Input and Output of Array

Values (continued)


8.2 Array Initialization

• Arrays , like scalar variables , can be

declared either inside or outside a function .

• Arrays declared inside a function are local

arrays, and arrays declared outside a

function are global arrays .


Array Initialization (continued)

#define SIZE1 20

#define SIZE2 25

#define SIZE3 15

int gallons[SIZE1]; /* a global array */

static int dist[SIZE2]; /* a static global array */

int main()

{

int miles[SIZE3]; /* an auto local array */

static int course[SIZE3]; /* static local array */

…

return 0;

}


• Array elements can be initialized within their declaration statements in the same manner as scalar variables, except that the initializing elements must be included in braces “{}”.

Examples of such initializations for automatic, static,

and global arrays are

int grades[5] = { 98, 87, 92, 79, 85 };

char codes[6] = { „s‟,„a‟,„m‟,„p‟,„l‟,„e‟};

double width[7] = { 10.96, 6.43, 2.58, .86, 5.89, 7.56, 8.22} ;

static int temp[4] = {10 , 20 , 30 , 40 } ;

static float temp[4] = { 98.6, 97.2, 99.0, 101.5} ;


• If the number of initializers is less than the

declared number of elements listed in

square brackets the initializers are applied

starting with array element 0 .

• Thus , in the declaration

float length[7] = { 7.8 , 6.4 , 4.9 , 11.2 };

• only length[0] , length[1] , length[2] and

length[3] are initialized with the listed values .

• The other array elements will be initialized to

zero.


• A unique feature of initializers is that the size of an array may be omitted when initializing values are included in the declaration statement .

• For example , the declaration

int gallons[ ] = { 16, 12, 10, 14, 11 } ;

reserves enough storage room for five elements.

• Similarly, the following two declarations are equivalent :

char codes[6] = { „s‟,„a‟,„m‟,„p‟,„l‟,„e‟};

char codes[ ] = { „s‟,„a‟,„m‟,„p‟,„l‟,„e‟};


• An interesting and useful simplification can

also be used when initializing character

arrays.

• For example, the declaration

char codes[ ] = “sample”; // no braces or commas

• uses the string “sample” to initialize the

codes array. ‘\0’ , is called the null character

The null character is automatically appended to all strings by the C compiler .


Array Initialization (continued)


8.3 Arrays as Function Arguments

• Individual array elements are passed to a

function by simply including them as

subscripted variables in the function call

argument list .

• For example , the function call

findMin(grades[2] , grades[6] ) ;

passes the values of the elements grades[2]

and grades[6] to the function findMin ( ).

Pass by Value / Pass by Reference?


Size can be omitted

Arrays as Function Arguments

(continued)


Arrays as Function Arguments

(continued)


Case Study: Computing Averages and

Standard Deviations

• Two statistical functions are created to

determine the average and standard

deviation, respectively, of an array of

numbers


Write the Functions


Write the Functions (continued)


8.5 Two-Dimensional Arrays

• A two-Dimensional array, which is sometimes

referred to as a table, consists of both rows and

columns of elements.

• For example, the array of numbers

• is a two-dimensional array of integers.

8 16 9 52

3 15 27 6

14 25 2 10

int val[3][4];


Two-Dimensional Arrays (continued)


The declaration of 2D Array

int val[3][4] = { { 8, 16, 9, 52 } ,

{ 3, 15, 27, 6 } ,

{ 14, 25, 2, 10 } } ;

• declares val to be an array of integers with three rows and four columns, with the initial values given in the declaration .

• The first set of internal braces contains the values for row 0 of the array, the second set of internal braces contains the values for row 1, and the third set of braces the values for row 2 .



int val[3][4] = { { 8, 16, 9, 52 } ,{ 3, 15, 27, 6 } ,{ 14, 25, 2, 10 } } ;

is similar


Row size can be omitted


void display (int nums[][COLS]

How it is different?


Internal Array Element Location

Algorithm (continued)

by Reddy & Ziegler 33

Larger Dimensional Arrays

• A three-dimensional array can be viewed as a book of data tables.

j = 0 j = 1 j = 2 j = 3

Rightmost subscript

i = 0

i = 1

i = 2

Middle subscript

k =1

k =0

Leftmost

subscript

3-D array of size [2][3][4]


Memory Location

a[0][0][0] a[1][0][0]

a[0][0][1] a[1][0][1]

a[0][0][2] a[1][0][2]

a[0][0][3] a[1][0][3]

a[0][1][0] a[1][1][0]

a[0][1][1] a[1][1][1]

a[0][1][2] a[1][1][2]

a[0][1][3] a[1][1][3]

a[0][2][0] a[1][2][0]

a[0][2][1] a[1][2][1]

a[0][2][2] a[1][2][2]

a[0][2][3] a[1][2][3]


Declaration and Storage Allocation

• Declaration of three-dimensional arrays requires

three indices: plane, row, and column.

• On each plane, the row and column indices are the

same and the plane index varies from one plane to

the next.

• The plane index varies from 0 to one less than the

number of planes, the row index varies from 0 to

one less than the number of rows, and the column

index varies from 0 to one less than the number of

columns.


Input of Three-Dimensional Arrays


Output of Three-Dimensional Arrays


Manipulation of Three-Dimensional Arrays


Common Programming Errors

• Forgetting to declare the array

• Using a subscript that references a nonexistent

array element

• Not using a large enough conditional value in a for

loop counter to cycle through all the array elements

• Forgetting to initialize the array


Common Compiler Errors


Summary

• A single-dimensional array is a data structure that

can store a list of values of the same data type

• Elements are stored in contiguous locations

– Referenced using the array name and a subscript

• Single-dimensional arrays may be initialized when

they are declared

• Single-dimensional arrays are passed to a function

by passing the name of the array as an argument


Summary (continued)

• A two-dimensional array is declared by listing both

a row and a column size with the data type and

name of the array

• Two-dimensional arrays may be initialized when

they are declared

• Two-dimensional arrays are passed to a function

by passing the name of the array as an argument

• Three-dimensional arrays (by Reddy & Ziegler)

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