Arrays

Define arrays. Explain the array types with an example program for each type.

Arrays are data structures which hold multiple variables of the same data type. Consider the case where a programmer needs to keep track of a number of people within an organization. So far, our initial attempt will be to create a specific variable for each user.

This might look like,

int name1 = 101; int name2 = 232; int name3 = 231;

It becomes increasingly more difficult to keep track of this as the number of variables increase. Arrays offer a solution to this problem. An array is a multi-element box, a bit like a filing cabinet, and uses an indexing system to find each variable stored within it. In C, indexing starts at zero. Arrays, like other variables in C, must be declared before they can be used. The replacement of the above example using arrays looks like,

int names[4]; names[0] = 101; names[1] = 232; names[2] = 231; names[3] = 0;

We created an array called names, which has space for four integer variables. You may also see that we stored 0 in the last space of the array. This is a common technique used by C programmers to signify the end of an array. Arrays have the following syntax, using square brackets to access each indexed value (called an element).

x[i]

so that x[5] refers to the sixth element in an array called x. In C, array elements start with 0. Assigning values to array elements is done by,

x[10] = g; and assigning array elements to a variable is done by, g = x[10];

In the following example, a character based array named word is declared, and each element is assigned a character. The last element is filled with a zero value, to signify the end of the character string (in C, there is no string type, so character based arrays are used to hold strings). A printf statement is then used to print out all elements of the array.

/* Introducing array's, 2 */

#include <stdio.h>

main()

{

char word[20]; word[0] = 'H'; word[1] = 'e'; word[2] = 'l'; word[3] = 'l'; word[4] = 'o'; word[5] = 0;

printf("The contents of word[] is -->%s\n", word );

}

DECLARING ARRAYS

Arrays may consist of any of the valid data types. Arrays are declared along with all other variables in the declaration section of the program.

/* Introducing array's */

#include <stdio.h>

main()

{

int numbers[100]; float averages[20]; numbers[2] = 10;

--numbers[2];

printf("The 3rd element of array numbers is %d\n", numbers[2]);

}

The above program declares two arrays, assigns 10 to the value of the 3rd element of array numbers, decrements this value ( --numbers[2] ), and finally prints the value. The number of elements that each array is to have is included inside the square brackets

ASSIGNING INITIAL VALUES TO ARRAYS

The declaration is preceded by the word static. The initial values are enclosed in braces,

Example:

#include <stdio.h>

main()

{

int x;

static int values[] = { 1,2,3,4,5,6,7,8,9 };

static char word[] = { 'H','e','l','l','o' };

for( x = 0; x < 9; ++x )

printf("Values [%d] is %d\n", x, values[x]);

}

MULTI DIMENSIONED ARRAYS

Multi-dimensioned arrays have two or more index values which specify the element in the array.

multi[i][j];

In the above example, the first index value i specifies a row index, whilst j specifies a column index.

DECLARATION

int m1[10][10];

static int m2[2][2] = { {0,1}, {2,3} };

sum = m1[i][j] + m2[k][l];

NOTE the strange way that the initial values have been assigned to the two-dimensional array m2. Inside the braces are,

{ 0, 1 },

{ 2, 3 }

Remember that arrays are split up into row and columns. The first is the row, the second is the column. Looking at the initial values assigned to m2, they are,

m2[0][0] = 0 m2[0][1] = 1 m2[1][0] = 2 m2[1][1] = 3

Example:

#include <stdio.h>

main()

{

static int m[][] = { {10,5,-3}, {9, 0, 0}, {32,20,1}, {0,0,8} };

int row, column, sum;

sum = 0;

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

for( column = 0; column < 3; column++ ) sum = sum + m[row][column]; printf("The total is %d\n", sum );

}

CHARACTER ARRAYS [STRINGS]

Consider the following program,

#include <stdio.h>

main()

{

static char name1[] = {'H','e','l','l','o'}; static char name2[] = "Hello"; printf("%s\n", name1);

printf("%s\n", name2);

}

The difference between the two arrays is that name2 has a null placed at the end of the string, ie, in name2[5], whilst name1 has not. To insert a null at the end of the name1 array, the initialization can be changed to,

static char name1[] = {'H','e','l','l','o','\0'};

Consider the following program, which initialises the contents of the character based array word during the program, using the function strcpy, which necessitates using the include file string.h

Example:

#include <stdio.h>

#include <string.h>

main()

{

char word[20];

strcpy( word, "hi there." );

printf("%s\n", word );

}