Chapter 6 arrays part-1

1
Chapter 6 - Arrays
Outline
6.1 Introduction
6.2 Arrays
6.3 Declaring Arrays
6.4 Examples Using Arrays
6.5 Passing Arrays to Functions
6.6 Sorting Arrays
6.7 Case Study: Computing Mean, Median and Mode Using
Arrays
6.8 Searching Arrays
6.9 Multiple-Subscripted Arrays

2
6.1 Introduction

Arrays
− Structures of related data items
− Static entity – same size throughout program
− Dynamic data structures discussed in Chapter 12

3
6.2 Arrays

Array
− Group of consecutive memory locations
− Same name and type

To refer to an element, specify
− Array name
− Position number

Format:
arrayname[ position number ]
− First element at position 0
– n element array named c:
• c[ 0 ], c[ 1 ]...c[ n – 1 ]
Name of array
(Note that all
elements of this
array have the
same name, c)
Position number
of the element
within array c
c[6]
-45
6
0
72
1543
-89
0
62
-3
1
6453
78
c[0]
c[1]
c[2]
c[3]
c[11]
c[10]
c[9]
c[8]
c[7]
c[5]
c[4]

4
6.2 Arrays

Array elements are like normal variables
c[ 0 ] = 3;
printf( "%d", c[ 0 ] );
− Perform operations in subscript. If x equals 3
c[ 5 - 2 ] == c[ 3 ] == c[ x ]

5
6.3 Declaring Arrays

When declaring arrays, specify
− Name
− Type of array
− Number of elements
arrayType
arrayName[ numberOfElements ];
− Examples:
int c[ 10 ];
float myArray[ 3284 ];

Declaring multiple arrays of same type
− Format similar to regular variables
− Example:
int b[ 100 ], x[ 27 ];

6

Initializers
int n[ 5 ] = { 1, 2, 3, 4, 5 };
− If not enough initializers, rightmost elements
become 0
int n[ 5 ] = { 0 }

All elements 0
− If too many a syntax error is produced syntax error
− C arrays have no bounds checking

If size omitted, initializers determine it
int n[ ] = { 1, 2, 3, 4, 5 };
− 5 initializers, therefore 5 element array

7
1. Initialize
array
2. Loop
3. Print
1 /* Fig. 6.8: fig06_08.c
2 Histogram printing program */
3 #include <stdio.h>
4 #define SIZE 10
5
6 int main()
7 {
8 int n[ SIZE ] = { 19, 3, 15, 7, 11, 9, 13, 5, 17, 1 };
9 int i, j;
10
11 printf( "%s%13s%17sn", "Element", "Value", "Histogram" );
12
13 for ( i = 0; i <= SIZE - 1; i++ ) {
14 printf( "%7d%13d ", i, n[ i ]) ;
15
16 for ( j = 1; j <= n[ i ]; j++ ) /* print one bar */
17 printf( "%c", '*' );
18
19 printf( "n" );
20 }
21
22 return 0;
23 }

8
Program
Output
Element Value Histogram
0 19 *******************
1 3 ***
2 15 ***************
3 7 *******
4 11 ***********
5 9 *********
6 13 *************
7 5 *****
8 17 *****************
9 1 *

9

Character arrays
− String “first” is really a static array of characters
− Character arrays can be initialized using string
literals
char string1[] = "first";

Null character '0' terminates strings
• string1 actually has 6 elements
− It is equivalent to
char string1[] = { 'f', 'i', 'r', 's', 't', '0' };
− Can access individual characters
string1[ 3 ] is character ‘s’
− Array name is address of array, so & not needed for
scanf
scanf( "%s", string2 );

Reads characters until whitespace encountered


10
1. Initialize
strings
2. Print
strings
2.1 Define
loop
2.2 Print
characters
1 /* Fig. 6.10: fig06_10.c
2 Treating character arrays as strings */
4
5 int main()
6 {
7 char string1[ 20 ], string2[] = "string literal";
8 int i;
9
10 printf(" Enter a string: ");
11 scanf( "%s", string1 );
12 printf( "string1 is: %snstring2: is %sn"
13 "string1 with spaces between characters is:n",
14 string1, string2 );
15
16 for ( i = 0; string1[ i ] != '0'; i++ )
17 printf( "%c ", string1[ i ] );
18
19 printf( "n" );
20 return 0;
21 }
Enter a string: Hello there
string1 is: Hello
string2 is: string literal
string1 with spaces between characters is:
H e l l o

11

Passing arrays
− To pass an array argument to a function, specify the
name of the array without any brackets
int myArray[ 24 ];
myFunction( myArray, 24 );

Array size usually passed to function
− Arrays passed call-by-reference
− Name of array is address of first element
− Function knows where the array is stored

Modifies original memory locations

Passing array elements
− Passed by call-by-value
− Pass subscripted name (i.e., myArray[ 3 ]) to

12

Function prototype
void modifyArray( int b[], int
arraySize );
− Parameter names optional in prototype
• int b[] could be written int []
• int arraySize could be simply int

13
1. Function
definitions
2. Pass array to
a function
2.1 Pass array
element to a
function
3. Print
1 /* Fig. 6.13: fig06_13.c
2 Passing arrays and individual array elements to functions */
4 #define SIZE 5
5
6 void modifyArray( int [], int ); /* appears strange */
7 void modifyElement( int );
8
9 int main()
10 {
11 int a[ SIZE ] = { 0, 1, 2, 3, 4 }, i;
12
13 printf( "Effects of passing entire array call "
14 "by reference:nnThe values of the "
15 "original array are:n" );
16
17 for ( i = 0; i <= SIZE - 1; i++ )
18 printf( "%3d", a[ i ] );
19
20 printf( "n" );
21 modifyArray( a, SIZE ); /* passed call by reference */
22 printf( "The values of the modified array are:n" );
23
24 for ( i = 0; i <= SIZE - 1; i++ )
25 printf( "%3d", a[ i ] );
26
27 printf( "nnnEffects of passing array element call "
28 "by value:nnThe value of a[3] is %dn", a[ 3 ] );
29 modifyElement( a[ 3 ] );
30 printf( "The value of a[ 3 ] is %dn", a[ 3 ] );
31 return 0;
32 }
Entire arrays passed call-by-
reference, and can be modified
Array elements passed call-by-
value, and cannot be modified

14
3.1 Function
definitions
33
34 void modifyArray( int b[], int size )
35 {
36 int j;
37
38 for ( j = 0; j <= size - 1; j++ )
39 b[ j ] *= 2;
40 }
41
42 void modifyElement( int e )
43 {
44 printf( "Value in modifyElement is %dn", e *= 2 );
45 }
Effects of passing entire array call by reference:
The values of the original array are:
0 1 2 3 4
The values of the modified array are:
0 2 4 6 8
Effects of passing array element call by value:
The value of a[3] is 6
Value in modifyElement is 12
The value of a[3] is 6

15
6.6 Sorting Arrays

Sorting data
− Important computing application
− Virtually every organization must sort some data

Bubble sort (sinking sort)
− Several passes through the array
− Successive pairs of elements are compared

If increasing order (or identical ), no change

If decreasing order, elements exchanged
− Repeat

Example:
− original: 3 4 2 6 7
− pass 1: 3 2 4 6 7
− pass 2: 2 3 4 6 7
−

Chapter 6 arrays part-1

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