2.2 ctype.h

The ctype header is used for testing and converting characters. A control character refers to a character that is not part of the normal printing set. In the ASCII character set, the control characters are the characters from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL). Printable characters are those from 0x20 (space) to 0x7E (tilde).

Functions:

isalnum();
isalpha();
iscntrl();
isdigit();
isgraph();
islower();
isprint();
ispunct();
isspace();
isupper();
isxdigit();
tolower();
toupper();


2.2.1 is... Functions

Declarations:

int isalnum(int character);
int isalpha(int character);
int iscntrl(int character);
int isdigit(int character);
int isgraph(int character);
int islower(int character);
int isprint(int character);
int ispunct(int character);
int isspace(int character);
int isupper(int character);
int isxdigit(int character);


The is... functions test the given character and return a nonzero (true) result if it satisfies the following conditions. If not, then 0 (false) is returned.

Conditions:

2.2.2 to... Functions

Declarations:

int tolower(int character);
int toupper(int character);


The to... functions provide a means to convert a single character. If the character matches the appropriate condition, then it is converted. Otherwise the character is returned unchanged.

Conditions:

Example:

#include<ctype.h>
#include<stdio.h>
#include<string.h>

int main(void)
{
  int loop;
  char string[]="THIS IS A TEST";

  for(loop=0;loop<strlen(string);loop++)
    string[loop]=tolower(string[loop]);

  printf("%s\n",string);
  return 0;
}