Week 10
This week just covers a bunch of character and string functions.
Character-handling Library (<ctype.h>)
Each function in the <ctype.h> library accepts an unsigned char (which can
be represented as an int) or EOF (EOF is usually -1) as input.
Character Type Checking Functions (digits, letters, hex)
isdigit(int c)
Returns true if c is a digit (0–9), otherwise returns false.
isalpha(int c)
Returns true if c is a letter (a–z or A–Z), otherwise returns false.
isalnum(int c)
Returns true if c is either a digit or a letter, otherwise returns false.
isxdigit(int c)
Returns true if c is a valid hexadecimal digit (0–9, a–f, A–F).
Case Checking and Conversion
islower(int c)
Returns true if c is a lowercase letter.
isupper(int c)
Returns true if c is an uppercase letter.
tolower(int c)
If c is an uppercase letter, returns its lowercase equivalent. Otherwise, returns c unchanged.
toupper(int c)
If c is a lowercase letter, returns its uppercase equivalent. Otherwise, returns c unchanged.
Whitespace and Control Checking
isblank(int c)
Returns true if c is a space or tab.
isspace(int c)
Returns true if c is any whitespace character (space, tab, newline, vertical tab, form feed, carriage return).
iscntrl(int c)
Returns true if c is a control character (e.g., newline, tab, backspace).
ispunct(int c)
Returns true if c is a printable character but not a space or alphanumeric character.
Printing Character Checking
A printing character is any character that results in a visible symbol on screen or paper. This includes letters, digits, punctuation, and symbols.
isprint(int c)
Returns true if c is any printable character, including space.
isgraph(int c)
Returns true if c is any printable character except space.
String Conversion Functions (<stdlib.h>)
The standard library provides functions that convert the initial part of a string to an integer or floating-point number. Parsing stops as soon as a character is encountered that is not valid for the specified number format.
If the input string does not start with a valid numeric sequence, the function
returns 0 and *endPtr is set to point to the original nPtr (input).
If the base (for functions that have a base) is set to 0 then the function will
auto-detect the base.
If the number starts with 0 it will be interpreted as octal.
If the number starts with 0x or 0X it will be interpreted as hex.
If there is no prefix it will be interpreted as decimal.
The base can be any number up to 36 (10 digits + 26 characters).
Each function takes a second argument endPtr, which is used to return a pointer
to the rest of the string (i.e., the character immediately after the parsed
number). If you don't need this information, you can pass NULL instead.
strtod(const char *nPtr, char **endPtr)
Converts nPtr to a double. Stops at the first invalid character and sets endPtr to point to it.
strtol(const char *nPtr, char **endPtr, int base)
Converts nPtr to a long. Accepts a numerical base (e.g., 10 for decimal, 16 for hex).
strtoul(const char *nPtr, char **endPtr, int base)
Converts nPtr to an unsigned long. Otherwise behaves like strtol.