Page 35 - C-Language

a = isdigit(c); /* Checks if c is a digit (0-9), returns zero here. */
a = isgraph(c); /* Checks if c has a graphical representation (any printing character except
space), returns non-zero here. */
a = islower(c); /* Checks if c is a lower-case letter (a-z), returns zero here. */
a = isprint(c); /* Checks if c is any printable character (including space), returns non-zero
here. */
a = isupper(c); /* Checks if c is a upper-case letter (a-z), returns zero here. */
a = ispunct(c); /* Checks if c is a punctuation character, returns zero here. */
a = isspace(c); /* Checks if c is a white-space character, returns zero here. */
a = isupper(c); /* Checks if c is an upper-case letter (A-Z), returns non-zero here. */
a = isxdigit(c); /* Checks if c is a hexadecimal digit (A-F, a-f, 0-9), returns non-zero here.
*/

C99

a = isblank(c); /* Checks if c is a blank character (space or tab), returns non-zero here. */

There are two conversion functions. These are named using the prefix 'to'. These functions take
the same argument as those above. However the return value is not a simple zero or non-zero but
the passed argument changed in some manner.

These conversion functions operate as shown, assuming the default C locale:

int a;
int c = 'A';

/* Converts c to a lower-case letter (a-z).
* If conversion is not possible the unchanged value is returned.
* Returns 'a' here.
*/
a = tolower(c);

/* Converts c to an upper-case letter (A-Z).
* If conversion is not possible the unchanged value is returned.
* Returns 'A' here.
*/
a = toupper(c);

The below information is quoted from cplusplus.com mapping how the original 127-character
ASCII set is considered by each of the classifying type functions (a • indicates that the function
returns non-zero for that character)

ASCII
characters iscntrl isblank isspace isupper islower isalpha isdigit isxdigit isalnum ispunct isgraph isprint
values

0x00 ..
NUL, (other control codes) •
0x08

0x09 tab ('\t') • • •

0x0A .. (white-space control codes:
• •
0x0D '\f','\v','\n','\r')

0x0E .. (other control codes) •

https://riptutorial.com/ 11