cs 1001 programming in c lecture 5

8/14/2019 CS 1001 Programming in C Lecture 5

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CS 1001 Programming in CLecture 5

Arrays


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Arrays in Action

are 2D arrays (matrices) of numbers:


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Array

An array is a set of variables,represented by a single name. The individual variables are called

elements and are identified by indexnumbers. The following example declares an

array with ten elements.int buf[10];


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Indexing

The first element in the array has anindex number of zero. Therefore, the array buf has tenelements, indexed from zero to nine.

buf[0]buf[1]

.

.buf[9]


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Accessing the Elements

To access an individual element in thearray, the index number follows thevariable name in square brackets.

The variable can then be treated likeany other variable in C. The following example assigns a value

6 to the first element in the array buf .buf[0] = 16;


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wArray

The example prints the value of thethird element in array buf .

printf("%d\n", buf[2]);

The example uses the scanf functionto read a value from the keyboard intothe last element of array buf .

scanf("%d", &x[9]);


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Initializing Array Elements

Arrays can be initialized like any othervariables by assignment.As an array contains more than one

value, the individual values are placedin curly braces, and separated withcommas.

The example initializes a tendimensional array with the first tenvalues of the three times table.int x[10] = {3, 6, 9, 12, 15, 18, 21, 24, 27, 30};


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Looping through an Array

As the array is indexed sequentially,we can use the for loop to display allthe values of an array.

The example displays all the values of an array.


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Example#include

void main (void)

{

int x[10]={3,6,9,12,15,18,21,24,27,30};

int i;

for(i=0; i


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Assignment

This saves assigning the values individuallyint x[10];x[0] = 3;x[1] = 6;

x[2] = 9;x[3] = 12;x[4] = 15;x[5] = 18;x[6] = 21;x[7] = 24;x[8] = 27;

x[9] = 30;


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Example

The program reads a line, stores it in abuffer, and prints its length (excludingthe newline at the end).


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void main(void )

{int n, c;

char line[100];

n = 0;

while( (c=getchar( )) != '\n' ) {

if( n < 100 )

line[n] = c;

n++;}

printf("length = %d\n", n);

}


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Working with Arrays

Example: adds up the elements of anarray:

int array[5]={2, 3, 4, 5,2}int sum = 0;for( i=0; i


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Arrays of Different Types

int ID[30];/* Could be used to store the IDnumbers of students in a class */

float temperatures[31];/* Could be used to store thedaily temperatures in a month */

char name[20];/* Could be used to store a

character string*/


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Multidimensional Arrays

An array can have more than onedimension.By allowing the array to have more

than one dimension provides greaterflexibility.Spreadsheets are built on a two

dimensional array; an array for therows, and an array for the columns.


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Example

The example uses a two dimensionalarray with two rows, each containingfive columns.


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#include

void main(){

/* Declare a 2 x 5 multidimensional array */

int x[2][5] = { {1, 2, 3, 4, 5},

{2, 4, 6, 8, 10} };int row, column;

for (row=0; row


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Storage in Memory

Since computer memory is essentially one-dimensional, with memory locations runningstraight from 0 up through the highestlocation in memory.

A multidimensional array cannot be stored inmemory as a grid. Instead, the array isdissected and stored in rows.Consider the two-dimensional array.


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Storage

---------row 0 | 1 | 2 | 3 |---------

row 1 | 4 | 5 | 6 |---------

row 2 | 7 | 8 | 9 |---------

To the computer, the array above actually "looks" like this:

--------------------------

| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |--------------------------| row 0 | row 1 | row 2 |

cs 1001 programming in c lecture 5

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