characters_strings.pdf

C Characters and Strings
Chapter 8

Outline
1. Introduction
2. Fundamentals of strings and characters
3. Character handling library
4. String conversion functions
5. Standard input/output library functions
6. The string handling library functions
2

3
Introduction
n Introduce some standard library functions
– Easy string and character processing
– Programs can process characters, strings, lines of text, and blocks of memory
n These techniques used to develop text-processing software as:
– Word processors
– Editors
In this chapter you will learn:
 T
o use the functions of the character-handling library (ctype)
 T
o use the string-conversion functions of the general utilities library (stdlib)
 T
o use the string and character input/output functions of the standard input/
output library (stdio)
 T
o use the string-processing functions of the string handling library (string)
 The power of function libraries as a means of achieving software reusability

Outline
1. Introduction
4

5
Fundamentals of strings and characters
Characters
– Building blocks of programs
• Every program is a sequence of meaningfully grouped characters
–Character constant  A character in single quotes
– a character is an integer (ASCII values range 0–255)
• 'z' represents the integer value of z
Strings
– Series of characters treated as a single unit
• Can include letters, digits and special characters (*, /, $)
–String literal (string constant)  Written in double quotes
• "Hello"
– A string is an array of characters
• A string is accessed via a pointer to the first character
• The value of a string is the address of first character

6
Fundamentals of strings and characters
String definitions
– Define as a character array or a variable of type char *
char
char
char
color[]
color[]
= "blue";
= {‘b’, ‘l’, ‘u’, ‘e’, ‘0’};
*colorPtr = "blue";
– Remember that strings represented as character arrays end with '0'
• color has 5 elements
Inputting strings
– Use scanf
scanf("%s", word);
• Copies input into word[] until a space, tab, newline or end-of-file
indicator
• Do not need & (because a string is a pointer)
Remember to leave room in the array for '0'

Outline
1. Introduction
7

8
Character handling library <ctype.h>
Character handling library
– Includes functions to perform useful tests and manipulations of
character data
– Each function receives a character (an int) or EOF as an argument
• The following slide contains a table of all the functions in <ctype.h>

9

10
/* Using functions isdigit, isalpha, isalnum, and isxdigit */
#include <stdio.h>
#include < ctype.h>
int main()
{
printf( "%sn%s%sn%s%snn", "According to isdigit: ",
isdigit( '8' ) ? "8 is a " : "8 is not a ", "digit",
isdigit( '#' ) ? "# is a " : "# is not a ", "digit" );
printf( "%sn%s%sn%s%sn%s%sn%s%snn",
"According to isalpha:",
isalpha( 'A' ) ? "A is a " : "A is not a ", "letter",
isalpha( 'b' ) ? "b is a " : "b is not a ", "letter",
isalpha( '&' ) ? "& is a " : "& is not a ", "letter",
isalpha( '4' ) ? "4 is a " : "4 is not a ", "letter" );
According to isdigit:
8 is a digit
# is not a digit
According to isalpha:
printf("According to isdigit:n");
if (isdigit( '8' ))
printf("8 is a digitn");
else
printf("8 is not a digitn");
printf("According to isdigit:n");
if (isdigit( '#' ))
printf("# is a digitn");
else
printf("# is not a digitn");
isdigit tests if a character is a
decimal digit
isalpha tests if a character is a letter
A is a letter
b is a letter
& is not a letter
4 is not a letter

Outline
1. Introduction
16

17
String conversion functions <stdlib.h>
n Conversion functions
Convert strings of digits to integer and floating-point values
– In <stdlib.h> (general utilities library)

String conversion functions <stdlib.h>

Outline
1. Introduction
24

25
Standard input/output library functions <stdio.h>
Functions in <stdio.h>
• Used to manipulate character and string data

Standard input/output library functions <stdio.h>

Outline
1. Introduction
31

32
The string handling library functions <string.h>
String handling library has functions to:
– Manipulate string data
– Search strings
– T
okenize strings
– Determine string length
String manipulation functions:

35
n Comparing strings
– Computer compares numeric ASCII codes of characters in string
int strcmp( const char *s1, const char *s2 );
– Compares string s1 to s2
– Returns a negative number if s1 < s2, zero if s1 == s2 or a positive
number if s1 > s2
int strncmp(
size_t n
const char *s1, const char
);
*s2,
– Compares up to n characters of string s1 to s2
– Returns values as above
Compaison functions:

36
/* Using strcmp and strncmp */
#include <stdio.h>
#include <string.h>
int main()
{
const char *s1 = "Happy New Year"; /* initialize char pointer */
const char *s2 = "Happy New Year"; /* initialize char pointer */
const char *s3 = "Happy Holidays"; /* initialize char pointer */
printf("%s%sn%s%sn%s%snn%s%2dn%s%2dn%s%2dnn",
"s1 = ", s1, "s2 = ", s2, "s3 = ", s3,
"strcmp(s1, s2) = ",
strcmp( s1, s2 )
strcmp( s1, s3 )
strcmp( s3, s1 )
,
,
);
printf("%s%2dn%s%2dn%s%2dn",
"strncmp(s1, s3, 6) = ",
"strncmp(s1, s3, 7) = ",
"strncmp(s3, s1, 7) = ",
strncmp( s1, s3, 6 )
,
,
);
return 0; /* indicates successful termination */
} /* end main */
strcmp compares
string s1 to string s2
strncmp compares the first 6
characters of string s1 to the first
6 characters of string s3
s1 = Happy
s2 = Happy
s3 = Happy
New Year
New Year
Holidays
s2) = 0
strcmp(s1,
strcmp(s1,
strcmp(s3,
s3) = 1
s1) = -1
strncmp(s1,
strncmp(s1,
strncmp(s3,
s3, 6) = 0
s3, 7) = 1
s1, 7) = -1

37
Search functions:

38
Search functions:

39
Search functions:
const char *string = "This is a test"; /* initialize char pointer */
char character1 = 'a'; /* initialize character1 */
char character2 = 'z'; /* initialize character2 */
'z' was not found in "This is a test".

45
/* Using strtok */
#include <stdio.h>
#include <string.h>
int main()
{
/* initialize array string */
char string[] = "This is a sentence with 7 tokens";
char *tokenPtr; /* create char pointer */
printf( "%sn%snn%sn",
"The string to be tokenized is:", string,
"The tokens are:" );
tokenPtr = strtok( string, " " ); /* begin tokenizing sentence */
/* continue tokenizing sentence until tokenPtr becomes NULL */
while ( tokenPtr != NULL ) {
printf( "%sn", tokenPtr );
tokenPtr = strtok( NULL, " " ); /* get next token */
} /* end while */
return 0; /* indicates successful termination */
} /* end main */
Search functions:
The string to be tokenized is:
This is a sentence with 7 tokens
The tokens are:
This
is
a
sentence
with
7
tokens
strtok “tokenizes” string by
breaking it into tokens at each space
Calling strtok again and passing it NULL
continues the tokenizing of the previous string
The function then finds the next
delimiting character in the string and
replaces it with a null ('0') character to
terminate the current token

46
Memory functions:
n Memory Functions
– In <string.h>
– Manipulate, compare, and search blocks of memory
– Can manipulate any block of data
n Pointer parameters are void *
–A pointer to any data type can be assigned to void *, and vice versa
–void * cannot be dereferenced
• Each function receives a size argument specifying the number of
bytes (characters) to process

47
Memory functions:

53
n size_t strlen( const char *s );
– Returns the number of characters (before the terminating
null character) in string s
char *strerror( int errornum );
– Creates a system-dependent error message based on
errornum
– Returns a pointer to the string
n
Other functions:

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