Module 4- Arrays and Strings

MODULE 4:ARRAYS AND
STRINGS
CO4. Demonstrate
the use of arrays,
strings and
structures in C
language.

CONTENTS
● Introduction to Arrays
● Declaration and initialization of one dimensional and two-
dimensional arrays.
● Definition and initialization of String
● String functions

INTRODUCTION TO ARRAYS
An array is a group of elements (data items) that have common
characteristics (eg numerical data, character data etc.,) and share a common
name. The elements of an array are differentiated from one another by their
positions within an array.
Each array element(i.e., each individual data item) is referred to by specifying
the array name followed by its subscript enclosed in square brackets.
The subscript indicates the position of the particular element with respect to
the rest of the elements.
The subscript must be a non negative integer.
For example, in the n element array , x, the array elements are
x[1],x[2],x[3],x[4],..........x[n-1],x[n];
and
1,2,......n are the subscripts x[i] refers to the ith element in a list of n
elements.

INTRODUCTION TO ARRAYS
Types of arrays
Single dimensional array
Multidimensional array

SINGLE DIMENSIONAL ARRAY
Declaration Of An Array
An array is declared in the same manner as ordinary variables, except
that each array name must be accompanied by a size specification.
This is necessary because the complier will have to know how much
memory to reserve for this array.
A single dimensional array is declared as follows :
type array_name[n];
where array_name is the name of an array of n elements of the type
specified. The size of an array must be an integer constant.
The integer array declaration
int x[100];
creates an array that is 100 elements along with the first element
being 0 and the last being 99.

The subscript used to declare an array is sometimes called a
dimension and the declaration for the
array is often referred to as dimensioning. The dimension used to
declare an array must always be a
positive integer constant, or an expression that can be evaluated to a
constant when the program is
compiled. It is sometimes convinient to define an array size in terms
of the symbolic constant. For
example, i[20]=1234;

An individual element in an array can be referred to by means of the
subscript, the number in brackets following the array name. A
subscript is the number that specifies the element’s position in an
array.
In the C language, subscript begins with zero. Thus, the valid
subscript value can be from 0 to n-1, if n is the dimension of the
array. The subscript value used to access an array element could
result from a subscription variable, a unary expression, a binary
expression etc. Thus, i[2] is not the second element of the array i but
the third.

int a[4];

INITIALIZING ARRAYS
An array can be initialized when declared by specifying the values of
some or all of its elements.
Arrays can be intialized at the time of declaration when their intial
values are known in advance.
The values to intialize an array must be constants never variables or
function calls. The array can be initialized as follows :
int array[5]={4,6,5,7,2};
float x[6]={0,0.25,0,-0.50,0,0};
When an integer array is declared as, int array[5]={4,6,5,7,2}; the
compiler will reserve ten contiguous bytes in memory to hold the five
integer elements as shown in the diagram below :

INITIALIZING ARRAYS
The array size need not be specified explicitly when intial values are
included as a part of an array declaration.
With a numerical array, the array size will automatically be set equal
to the number of initial values included within the declaration.
int digits[]={1,2,3,4,5,6};
float x[]={0,0.25,0,-0.5};
So digits will be a six-element integer array, and x will be a four-
element floating-point array. The individual elements will be assigned
the following values.
The example given below illustrates this point.
digits [0]=1;digits[1]=2;digits[2]=3;
digits[3]=4;digits[4]=5 ;digits[5]=6;

INITIALIZING ARRAYS
An array may also be intialized as follows : int
xyz[10]={78,23,67,56,87,76};
In the above array initialization, although the array size is 10, values
were defined only for the first six elements.

INITIALIZING ARRAYS
Example
int a[4]={4, 3, 2, 1};
/*Intializing and printing the value*/

INITIALIZING ARRAYS
#include<stdio.h>
int main()
{
int i,a[4]={4,3,2,1};
for(i=0;i<4;i++)
{
printf("a[%d]=%dn",i,a[i]);
printf("Address of a[%d] is %un",i,&a[i]);
}
return 0;
}

ARRAY OVERFLOW
It is illegal to access a non-existent element of the array. C does not
check for array overflow.
It is the programmers responsibility to ensure that any subscription
performed does not crosses the upper as well as the lower bounds of
the array.
int array[5];
array[5]=105; /* illegal as valid subscripting ends at array[4] */
In the above code, an attempt is made to move the binary value of
105 onto the 2 bytes that immediately follow the end of the array.
So when executing the assignment array[5]=105, some other
variables that the program uses are being overwritten.

PROCESSING AN ARRAY
If a and b are two similar arrays of the same data type, same
dimensions and same size then assignment operations and
comparison operations etc, must be carried out on an element-by-
element basis.
This is done within a loop, where each pass through the loop is used
to process an element of the array.
The number of passes through the loop will there for equal to the
number of array elements to be processed; and the value of the index
(subscript) would be incremented from 0 to n-1.

MULTIDIMENSIONAL ARRAYS
C as a language provides for arrays of arbitrary dimensions. A two
dimensional array of size m rows by n columns is declared as follows :
type array_name[m][n];
A two dimensional array, of type int, with 3 rows and 4 columns is
declared as follows
The array can be declared by passing values of number of rows and
number of columns as subscript values.
Example
int a[3][4];

INITIALIZING ARRAYS
The values can also be initialized by forming group of initial values
enclosed within braces.
The values within an inner pair of braces will be assigned to the
element of a row or all the values can be given in single braces
sequentially.
Example
int array[3][4] = {{0, 1, 2, 3}, {4, 5, 6, 7}, {8, 9, 10, 11}};
Or
int array[3][4] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};

PROCESSING AN ARRAY
The array processing is done as in the one dimensional array.
Since it is a two dimensional array we may need two variable to keep
track and to process the data in the array.

CHARACTER ARRAYS (STRINGS)
C Strings are nothing but array of characters ended with null character (‘0’).
This null character indicates the end of the string.
Strings are always enclosed by double quotes.
Whereas, character is enclosed by single quotes in C.
char string[20] = {‘f’, ’r’, ‘e’, ‘s’, ‘h’, ‘2’, ‘r’, ‘e’, ‘f’, ’r’, ‘e’, ‘s’, ‘h’, ‘0’};
(or)
char string[20] = “fresh2refresh”;
(or)
char string [] = “fresh2refresh”;
Difference between above declarations are, when we declare char as
“string[20]”, 20 bytes of memory space is allocated for holding the string
value.
When we declare char as “string[]”, memory space will be allocated as per the
requirement during execution of the program.

CHARACTER ARRAYS (STRINGS)
Declaration Of An Array
Array declaration is also done as same as normal array except for the
specification of character data type.
Example
char a[5];

INITIALIZATION OF CHARACTER
ARRAYS
Character array can be initialized in two different ways.
Firstly, they may initialize in the same way as the numeric array are
initialized.
char a[5] = {'H','a','r','i','0'};
(i.e.) by specifying character constants for each of the values. When
initializing character by character,
the null character ('0') should also be specified.
Secondly, character array can also be initialized as follows,
char a[5] ="Hari";
This type of initialization will include a provision for null character,
which is automatically added at the end of the string.

PROCESSING A CHARACTER
ARRAY
Character arrays are different from the numerical array. The entire
character string can be entered from the terminal and placed in a
character array. Whereas numeric arrays can be input element by
element only.
Same is the case with output also. The entire string can be output
using printf() function whereas an integer array can be output
element by element only.

PROCESSING A CHARACTER
ARRAY
#include<stdio.h>
#include<string.h>
int main ()
{
char a[6] ="Nikhat";
printf ("Name=%sn",a);
}

PASSING STRINGS TO FUNCTION
As strings are character arrays, so we can pass strings to function in a
same way we pass an array to a function.

PASSING STRINGS TO FUNCTION
// C program to illustrate how to
// pass string to functions
#include<stdio.h>
void printStr(char str[])
{
printf("String is : %s",str);
}
int main()
{
// declare and initialize string
char str[] = “nikhat";
// print string by passing string
// to a different function
printStr(str);
return 0;
}

STRING FUNCTIONS
Include string.h library to your program to use some of the inbuilt
string manipulation functions present in the library.there are about
20-22 inbuilt string manipulating functions present in this library.
The most common functions used from the library are:
1. strlen("name of string")
2. strcpy( dest, source)
3. strcmp( string1, string2 )
4. strstr( str1, str2 )
Commonly Used String Functions
strlen() - calculates the length of a string
strcpy() - copies a string to another
strcmp() - compares two strings
strcat() - concatenates two strings

STRING FUNCTIONS
The strlen() function takes a string as an argument and returns
its length. The returned value is of type size_t (the unsigned
integer type).
It is defined in the <string.h> header file.
#include <stdio.h>
#include <string.h>
int main()
{
char str1[20] = “nikhat";
printf("Length of string str1: %d", strlen(str1));
return 0;
}

STRING FUNCTIONS
strcmp()
int strcmp(const char *str1, const char *str2)
It compares the two strings and returns an integer value. If both
the strings are same (equal) then this function would return 0
otherwise it may return a negative or positive value based on the
comparison.
If string1 < string2 OR string1 is a substring of string2 then it
would result in a negative value. If string1 > string2 then it
would return positive value.
If string1 == string2 then you would get 0(zero) when you use
this function for compare strings.

STRING FUNCTIONS
#include <stdio.h>
#include <string.h>
int main()
{
char s1[20] = “nikhat";
char s2[20] = “shaikh";
if (strcmp(s1, s2) ==0)
{
printf("string 1 and string 2 are equal");
}else
{
printf("string 1 and 2 are different");
}
return 0;
}

STRING FUNCTIONS
Return value
- if Return value if < 0 then it indicates str1 is less than str2
- if Return value if > 0 then it indicates str2 is less than str1
- if Return value if = 0 then it indicates str1 is equal to str2

STRING FUNCTIONS
strcat()
char *strcat(char *str1, char *str2)
It concatenates two strings and returns the concatenated string.
#include <stdio.h>
#include <string.h>
int main()
{
char s1[10] = "Hello";
char s2[10] = "World";
strcat(s1,s2);
printf("Output string after concatenation: %s", s1);
return 0;
}

STRING FUNCTIONS
strcpy()
char *strcpy( char *str1, char *str2)
It copies the string str2 into string str1, including the end character
(terminator char ‘0’).
#include <stdio.h>
#include <string.h>
int main()
{
char s1[30] = "string 1";
char s2[30] = "string 2 : I’m gonna copied into s1";
/* this function has copied s2 into s1*/
strcpy(s1,s2);
printf("String s1 is: %s", s1);
return 0;
}

STRING FUNCTIONS
strstr(str1, str2)
This library function finds the first occurrence of the substring str2 in
the string str1. The terminating '0' character is not compared.
strstr( str1, str2);
- str1: the main string to be scanned.
- str2: the small string to be searched in str1
This function is very useful in checking whether str2 is a substring of str1 or
not.
Return value
This function returns a pointer to the first occurrence in str1 of any of the
entire sequence of characters specified in str2, or a NULL pointer if the
sequence is not present in str1.
.

STRING FUNCTIONS
#include<stdio.h>
#include<string.h>
int main ()
{
char str1[55] ="This is a test string for testing";
char str2[20]="test";
char *p;
p = strstr (str1, str2);
if(p)
{
printf("string foundn" ); //i.e str2 is a substring of str1.
printf ("First occurrence of string "test" in "%s" is" " "%s"",str1, p);
}
else
printf("string not foundn" ); // str2 is not a substring of str1.
return 0;
}

Module 4- Arrays and Strings

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Module 4- Arrays and Strings