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Character classification functions
Category Functions
Letters isalpha( )
Lowercase letters islower( )
Uppercase letters isupper( )
Decimal digits isdigit( )
Hexadecimal digits isxdigit( )
Letters and decimal digits isalnum( )
Printable characters (including whitespace) isprint( )
Printable, non-whitespace characters isgraph( )
Whitespace characters isspace( )
Whitespace characters that separate words in a line of text isblank( )
Punctuation marks ispunct( )
Control characters iscntrl( )

The functions isgraph() and iswgraph() behave differently if the execution character set contains other byte-coded, printable, whitespace characters (that is, whitespace characters which are not control characters) in addition to the space character (' '). In that case, iswgraph() returns false for all such printable whitespace characters, while isgraph() returns false only for the space character (' ').

Case mapping functions

The functions listed in [link] yield the uppercase letter that corresponds to a given lowercase letter, and vice versa. All other argument values are returned unchanged.

Character conversion functions
Conversion Functions in ctype.h
Upper- to lowercase tolower( )
Lower- to uppercase toupper( )

String processing functions

A string is a continuous sequence of characters terminated by '\0', the string terminator character. The length of a string is considered to be the number of characters before the string terminator. Strings are stored in arrays whose elements have the type char or wchar_t. Strings of wide characters that is, characters of the type wchar_tare also called wide strings .

C does not have a basic type for strings, and hence has no operators to concatenate, compare, or assign values to strings. Instead, the standard library provides numerous functions, listed in

[link] to perform these and other operations with strings. The header string.h declares the functions for conventional strings of char. The names of these functions begin with str.

Like any other array, a string that occurs in an expression is implicitly converted into a pointer to its first element. Thus when you pass a string as an argument to a function, the function receives only a pointer to the first character, and can determine the length of the string only by the position of the string terminator character.

String-processing functions
Purpose Functions
Find the length of a string. strlen( )
Copy a string. strcpy( ), strncpy( )
Concatenate strings. strcat( ), strncat( )
Compare strings. strcmp( ), strncmp( ), strcoll( )
Transform a string so that a comparison of two transformed strings using strcmp( ) yields the same result as a comparison of the original strings using the locale-sensitive function strcoll( ). strxfrm( )
In a string, find:
- The first or last occurrence of a given character strchr( ), strrchr( )
- The first occurrence of another string strstr( )
- The first occurrence of any of a given set of characters strcspn( ), strpbrk( )
- The first character that is not a member of a given set strspn( )
Parse a string into tokens strtok( )
#include<stdio.h>#include<conio.h>#include<string.h>// You must declare the library string.h // to use functions strcpy, strcmp...void main() {char str1[10] = “abc”;char str2[10] = “def”;clrscr(); printf(“ str1: %s”,str1);printf(“\n str2: %s”,str2); printf(“\n strcmp(str1,str2) = %d”,strcmp(str1,str2));printf(“\n strcat(str1,str2) = %s”,strcat(str1,str2)); printf(“\n str1: %s”,str1);printf(“\n str2: %s”,str2); printf(“\n strcpy(str1,str2) = %s”,strcpy(str1,str2));printf(“\n str1: %s”,str1); printf(“\n str2: %s”,str2);strcpy(str1,”ab”); strcpy(str2,”abc”);printf(“\n strcmp(str1,str2) = %d”,strcmp(str1,str2)); getch();}
Got questions? Get instant answers now!

here is the sample session with the above program

str1: abc str2: defstrcmp(str1,str2) = -3 strcat(str1,str2) = abcdefstr1: abcdef str2: defstrcpy(str1,str2) = def str1: defstr2: def strcmp(str1,str2) = -3

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Source:  OpenStax, Introduction to computer science. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10776/1.1
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