5 2. string processing

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 String
– String is a simple array of chars (characters)

– String is one-dimensional array of char

– The null character ‘0’ must be included at the end of String

– Various built-in functions are provided for String function

2

The End-of-String Sentinel ‘0’

 How to define String

char word[100];
word[0] = ‘a’;
word[1] = ‘b’;
word[2] = ‘c’;
word[3] = ‘0’; /* Insert null char at the end of a string*/

– 3 letters are stored in 3 byte but the null character need one
extra byte i.e., 4 bytes.

3

Initialization of Strings

 Use array name
– Use char array for processing string

[Ex] char word[4] = “abc”;

[Ex] char word[4] = {‘a’, ‘b’, ‘c’, ‘0’ };

[Ex] char word[] = {‘a’, ‘b’, ‘c’, ‘0’ };

[Ex] char word[] = “abc”; 4 chars are automatically
generated by the compiler

4

Displaying String and characters

 printf()
– Use %s for a string output
– Return the number of the printed string if the
output is successful, if not return -1

[Ex] int nchars;
char p[ ] = “Hello! the world”;
Hello! the world
num of chars = 16
nchars = printf(“%s”, p);
printf(“nnum of chars=%dn”, nchars);

5

Displaying String and characters

 puts()
– Faster and simpler than printf()
– After printing a string, automatically move to the next line

int puts(char *str); /*function prototype */

return
- no. of chars written if successful
- EOF(-1) if not

[Ex] char p[ ] = “Hi !!”;
puts(p);
puts(“Hello!!”); Hi !!
Hello!!

6

Reading Strings from the KB

 scanf()
– %s : Read until next whitespace (blank) character
– %ns : Read n characters, provided that it reads until the
whitespace as the space is found

int scanf(char *format, argument_list);

return
- no. of successfully matched and input items
-0 if not

7


Input: SKKU Univ.
[Ex] char name[80];

scanf(“%s”, name); /* name <- SKKU */

Input: C-Program is
[Ex] char name[80];
Read 3 characters
scanf(“%3s”, name); /* name <= C-P */
scanf(“%8s”, name); /* name <= rogram */
Read until a white space

8


 gets()
– Read string from Keyboard (KB) until ‘n’ is entered
– ‘n’ is automatically converted into ‘0’ at the end of string
As string is entered through scanf() :
• It skips leading whitespace characters
(It’s impossible to read whitespace.)
• It cannot enter ‘n’ in string.

char* gets(char *format);

return
- the address of the string
- NULL if EOF (end-of-file)

9


Exit as <blank line> or
<[ctrl] + D> are inputted
[Ex] char data[81];
or while(gets(data) != 0)
while( gets(data) != NULL) {
printf(“%sn”, data);
Printing Program with many lines
} on the screen until ALT+D is entered

10


 As you enter more characters than the size of
an arrary…
– What is output value as “abcde” is entered?
char a[4], b[4]=“1234”;

scanf(“%s”, a);
printf( “%s %sn”, a, b ) ;

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String-Handling Functions

 String Assign Function

[Ex] char str1[10] = “abc”, str2[10];
str1 = “123” ;
str2 = str1 ;

OK?? Why not??

12


 char *strcpy(char *s1, const char *s2);
– Copy s1 string into s2 string
– This function returns a pointer to the string s1.
– s1 must be appropriately allocated for storing the string.

[Ex] char str1[10] = “abc”, str2[10];
strcpy( str1, “abc” ) ;
strcpy( str2, str1 ) ;

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 String Comparison Function

[Ex] char str1[10], str2[10];
scanf( “%s”, str1 ) ;

if( str1 == str2 ) printf( “Same!!n” ) ;

OK?? Why not??

14


 int strcmp(const char *s1, const char *s2);
– Compares s1 string to s2 string
– return value < 0 : if s1 is less than s2 ASCII
– return value = 0 : if s1 and s2 are equal
– return value > 0 : if s1 is greater than s2 ASCII

[Ex] char str1[10], str2[10];

if( strcmp(str1,str2) == 0 ) printf( “Same!!n” ) ;

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 String Length

[Ex] char str1[10] ;

– How many letters do string str1 have?

int length ;
for( length = 0 ; s[length] != NULL ; length++ ) ;
printf( “The length of string: %dn”, length ) ;

16


 int strlen(const char *s1);
– Returns a length of the string

int length ;
printf( “The length of string: %dn”, strlen(str1) ) ;

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 Other String Functions
– strcat : Appends the string s2 to the end of string s1
– strchr : Searches for the first occurrence of c1 in s1
– strstr : Finds the first occurrence of the entire s2 in s1

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 char *strcat(char *s1, const char *s2);
– Concatenate string s2 onto the end of string s1
– Return s1
– String s1 must be appropriately allocated for storing the
string.

char str1[10]="1234";
char str2[10]="abcd";

strcat(str1, str2);
printf(“%s, %sn", str1, str2);

strcat(str2, “efgh” ) ;
printf(“%sn", str2);

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 char* strchr(const char *s1, char c1);
– Searches for the first occurrence of c1 in s1
– If c1 does not match, NULL pointer is returned.

[Ex] char str[10] ;

scanf( “%s”, str ) ;

if( strchr(str, ‘e’ ) != NULL )
printf( “e is foundn” );
else
printf( “e is not foundn” ) ;

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 char* strstr(const char *s1, char* s2);
– Finds the first occurrence of the entire s2 in s1
– If s1 does not match, NULL pointer is returned.

[Ex] char str[10] ;

scanf( “%s”, str ) ;

if( strchr(str, “” ) != NULL )
printf( “hi is foundn” );
else
printf( “hi is not foundn” ) ;

21

5 2. string processing

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5 2. string processing