C programming - String

String
5/21/2015 3:26 PM1 Prepared by Achyut Devkota
Achyut Devkota
Kathford International College

String
5/21/2015 3:26 PMPrepared by Achyut Devkota2
 A group of characters
 A string constant is a one-dimensional array
of characters terminated by a null ( ‘0’ ).
declaration of Character:
char mychar;
declaration of String:
char myString[10];
The characters after the null character are
ignored.

Initialization String
Initialization Syntax:
char myString [] = { 'H','A','E','S', 'L', 'E', 'R', '0' } ;
char myString[13] = “Initial value”
char myString[] = “Initial value”;
0 = null character
Note: that ‘0’ and ‘0’ are not same.
 When declaring a string don’t forget to leave a
space for the null character which is also
known as the string terminator character
Compilation time
initialization
n i t i a l v a l u e ? ? …I 0

Why Null
char ?
only way the functions that work with
a string can know where the string
ends.
n i t i a l v a l u e ? ? …I 0
char myString[100] = “Initial value”

Initialization String
Run time
Initialization
Character array :
Using Input/ output function :
Scanf() gets() getchar()

Common Error
The following results in an error:
1. char str1 [5]=“Hello”;
2. char str1[6];
ctr1=“Hello”;
3. char str1[6] = “Hello”;
char str2[6];
str2 = str1;
//Results in Error

Input Function
 The scanf() Function
 header file stdio.h
 Syntax:
char mystring[100];
scanf(“%s”, mystring);
 The name of a string is a pointer constant to the
first character in the character array.
 Problem:
terminates its input on the first white space it
finds.
white space includes blanks, tabs, carriage
returns(CR), form feeds & new line.

Example:
Output:

Input Function
 The gets() Function
 Header file stdio.h
 takes a string from standard input and assigns
it to a character array.
 It replaces the n with 0.
 Syntax:
char mystring[100];
gets(myString);
fgets() it keeps the n and includes it as part of the string.

Example:
Output:

Input Function
 The getchar() Function
 Takes single character at a time.
 Syntax:
char mychar;
mychar=getchar();
It can use to read each character of an string.
int i;
char mystring[100];
printf("Enter String:n");
for(i=0;i<10;i++)
mystring[i]=getchar();
mystring[9]='0';
printf("nn%s",mystring);
Example
:

Example:
What should be the output if entered string
is:
Hello boys

Output function
 The printf () function
(self study)
 The puts() function

Output function
 The putchar() Function
 output single character at a time.
 Syntax:
char mychar;
mychar=getchar();
It can use to read each character of an string.
Example int i;
char mystring[100];
printf("Enter String:n");
gets(mystring);
for(i=0;i<20;i++)
putchar(mystring[i]);

Example:
Rarely use in array
manipulation .

String operation – string.h
 Four main library function which is define in
string.h header file
strcpy() - copy one string into another
strcat() - append one string onto the right side of
the other
strcmp() – compare alphabetic order of two
strings
strlen() – return the length of a string

strcpy()
 strcpy(destinationstring, sourcestring)
 Copies sourcestring into destinationstring
 For example
Output

strcat()
 strcat() function to combine two strings into a new
string.
 strcat(destinationstring, sourcestring)
 appends sourcestring to right hand side of
destinationstring
 We need to be certain that the array to which we
assign the resulting string is large enough to hold all
the characters from the two contributing strings.
 Syntax:
strcat(str1, str2);

Example: strcat()
Output

strcmp()
 Compares str1 and str2 alphabetically
strcmp(str1, str2)
 If the two strings are equal, strcmp() returns 0.
 If str1 is greater than str2, strcmp() returns a
positive number.
 If str1 is less than str2, strcmp() returns a
negative number.

strcmp()

Example:
Output

strlen()
 Strlen() function to determine the length of
a string.
 It counts the number of characters in a string,
excluding the null character.
 Syntax:
strcount = strlen(myString);

Example:
Output:

More …
 strlwr() : converts a string to lowercase
 Strupr() : converts a string to uppercase
 Strncat() : Appends first n characters of a string
at the end of another
 Strncmp() :Compares first n characters of two
strings
 Strcmpi():Compares two strings without regard
to case ("i" denotes that this function ignores
case)
 Strrev() :Reverses string
 Strncpy() : copy first n character of one string to
another.

Example:
Output:

Problem:
 Write a program to input a string and
rearrange the string in alphabetical order. For
example, the word NEPAL should be written
as AELNP

What is the key difference between
‘A’ and “A” ?
 The representation of a char (e.g., ‘A’) and a string
(e.g., “A”) is essentially different.
 A string is an array of characters ended with the null
character.
A
Character ‘Q’
A 0
String “Q”

Two dimensional- string array
 An array of strings is a two-dimensional array
of characters in which each row is one string.
char names[std_number][Name_Lth];
char month[5][10] = {“January”,
“February”, “March”, “April”,
“May”};

Example:
Output

C programming - String

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