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 Arrays and Strings

Introduction

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Many applications require multiple data items that have

common characteristics. – In mathematics, we often express such groups of data

items in indexed form:

  • x1 , x , x! , ", xn 

 #rray is a data structure which can represent a collection of

data items which have the same data type $float%int%char&

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 Example: Finding Minimum of Numbers

  3 numbers

if ((a

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The Problem

'uppose we have 1( num)ers to handle.

 *r (.

 *r 1((.

+here do we store the num)ers -se 1(( varia)les

ow to tac/le this pro)lem

 'olution:

 – -se arrays.

0onstruct one varia)le $called array or su)scripted varia)le&capa)le of storing or holding all the hundred $any no& values.

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 Arrays

 #n array is a collective name given to a group of similar

quantities2. +hat is important is that the quantities must )e similar2

percentage mar/s of 1(( students

or salaries of !(( employees, or 

ages of 3( employees.

4hese similar elements could )e all ints, or all floats, or all

chars, etc.

-sually, the array of characters is called a string2, whereas

an array of ints or floats is called simply an array.

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Using Arrays

 #ll the data items constituting the group share the same

name.int x51(67

 Individual elements are accessed )y specifying the index

i.e. 8ach mem)er in the group is referred to )y its position in

the group.  In 0 the counting of elements )egins with ( and not with 1.

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Delaring Arrays

Like variables, the arrays that are used in a program

must be declared before they are used. General syntax:

  type arrayname !si"e#$

 – type specifies the type of element that %ill becontained in the array &int, float, char, etc.'

   – si"e is an integer constant %hich indicates the

maximum number of elements that can be stored

inside the array

 int marks!(#$

 – marks is an array containing a maximum of (

integers.

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 )xamples:

int x!*+#$char line!+#$

float points!*(+#$

char name!3(#$

If %e are not sure of the exact si"e of the array, %e can

define an array of a large si"e.

int marks!(+#$

though in a particular run %e may only be using, say, *+elements.

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!o" an array is stored in memory#

-tarting from a given memory location, the successive

array elements are allocated space in consecutive memorylocations.

• x: starting address of the array in memory

• k: number of bytes allocated per array element

 – a!i# is allocated memory location at address x i/k

int a!*+#$ starting address is *+0+

then a!4# is allocated memory location at address *+0+ 4/0

i.e. 0+0

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Aessing Array Elements

1 particular element of the array can be accessed by

specifying t%o things:

 – 2ame of the array.

 – Index &relative position' of the element in the array.

In , the index of an array starts from "ero.

)xample:

 – 1n array is defined as int x!*+#$

 – he first element of the array x can be accessed as

x!+#, fourth element as x!3#, tenth element as x!5#,etc.

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A $arning 

In , %hile accessing array elements, array bounds arenot checked.

)xample:

int marks!(#$:

:

marks!# 6 7($

 – he above assignment %ould not necessarily cause anerror.

 – 8ather, it may result in unpredictable program results.

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%nitiali&ation of Arrays

General form:

type arrayname!si"e# 6 9 list of values $ )xamples:

int marks!(# 6 970, 3, ;(, +, 7;$

char name!4# 6 9

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'ontd(

 – he si"e may be omitted. In such cases the compiler

automatically allocates enough space for all initiali"edelements.

int flag! # 6 9*, *, *, +$

char name! # 6 9

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!o" to read the elements into array#

?y reading them one element at a time

for &@6+$ @A0($ @'

scanf &BCfD, Ea!@#'$

he ampersand &E' is necessary.

he elements can be entered all in one line or in

different lines.

 Fou cannot directly scanf or printf arrays

printf &BD, a'$

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!o" to print the elements of an array#

?y printing them one element at a time.

for &@6+$ @A0($ @'

printf &BHn CfD, a!@#'$

 – he elements are printed one per line.

printf &BHnD'$

for &@6+$ @A0($ @'

printf &B CfD, a!@#'$

 – he elements are printed all in one line &starting

%ith a ne% line'.

i fi d * b i d b

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"rite a program to find a)erage mar*s obtained by a

lass of +, students in a test(

void main$ &

9int avg, sum ( 7

int i 7

int mar/s5!(6 7 %; array declaration ;%

for $ i ( 7 i > &

9

printf $ ?@n8nter mar/s ? & 7

scanf $ ?Ad?, Bmar/s5i6 & 7 %; store data in array ;%

C

for $ i ( 7 i > &

sum sum > mar/s5i6 7 %; read data from an array;%

avg sum % !( 7

printf $ ?@n#verage mar/s Ad?, avg & 7

C

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'harater Arrays and Strings

char !# 6 9 a, b, h, i, @, i, t, H+ $

!+# gets the value a, !*# the value b, and so on. he

last &7th' location receives the null character terminated character arrays are also called strings.

-trings can be initiali"ed in an alternative %ay. he lastdeclaration is eJuivalent to:

  char !# 6 Kabhi@itK$

he trailing null character is missing here. automaticallyputs it at the end.

2ote also that for individual characters, uses single

Juotes, %hereas for strings, it uses double Juotes.