Strings and characters

A program may contain character constants.
The value of a character constant is the integer value.
There is a table that represents the ASCII character set.
A string is a series of characters treated as a single unit
A string in C is an array of characters ending in the NULL character ('\0’).
- char colour[] = "Blue";
- const char *colour = "Blue";
- const char *colour = {'B', 'l', 'u', 'e', '\0'};
Make sure that char arrays are big enough when reading data (eg. scanf("%s", word);

Character Handling Library <ctype.h>

These functions return a nonzero (true) value if the given character satisfies the condition; otherwise, they return 0 (false).

Function	Description
`isalnum(int c)`	Checks if `c` is an alphanumeric character (letter or digit).
`isalpha(int c)`	Checks if `c` is a letter (uppercase or lowercase).
`isascii(int c)`	Checks if `c` is a valid ASCII character (0-127).
`isblank(int c)`	Checks if `c` is a blank character (space or tab).
`iscntrl(int c)`	Checks if `c` is a control character.
`isdigit(int c)`	Checks if `c` is a digit (`0-9`).
`isgraph(int c)`	Checks if `c` is a printable character, excluding space.
`islower(int c)`	Checks if `c` is a lowercase letter (`a-z`).
`isprint(int c)`	Checks if `c` is a printable character, including space.
`ispunct(int c)`	Checks if `c` is a punctuation character.
`isspace(int c)`	Checks if `c` is a whitespace character (space, tab, newline, etc.).
`isupper(int c)`	Checks if `c` is an uppercase letter (`A-Z`).
`isxdigit(int c)`	Checks if `c` is a hexadecimal digit (`0-9`, `A-F`, `a-f`).

These functions return the converted character if applicable; otherwise, they return the input character unchanged.

Function	Description
`tolower(int c)`	Converts `c` to lowercase if it is an uppercase letter.
`toupper(int c)`	Converts `c` to uppercase if it is a lowercase letter.

Function	Description
`int atoi(const char *str)`	Converts `str` to an `int`.
`long atol(const char *str)`	Converts `str` to a `long` integer.
`long long atoll(const char *str)`	Converts `str` to a `long long` integer.
`int strtol(const char str, char *endptr, int base)`	Converts `str` to a `long` integer with a specified base (e.g., binary, decimal, hexadecimal).
`long strtoll(const char str, char *endptr, int base)`	Converts `str` to a `long long` integer with a specified base.
`unsigned long strtoul(const char str, char *endptr, int base)`	Converts `str` to an `unsigned long` integer with a specified base.
`unsigned long long strtoull(const char str, char *endptr, int base)`	Converts `str` to an `unsigned long long` integer with a specified base.

Function	Description
`double atof(const char *str)`	Converts `str` to a `double`.
`double strtod(const char str, char *endptr)`	Converts `str` to a `double` and sets `endptr` to point to any remaining characters.
`float strtof(const char str, char *endptr)`	Converts `str` to a `float`.
`long double strtold(const char str, char *endptr)`	Converts `str` to a `long double`.

Function	Description
`int printf(const char *format, ...)`	Prints formatted output to `stdout`.
`int scanf(const char *format, ...)`	Reads formatted input from `stdin`.
`int putchar(int c)`	Writes a single character to `stdout`.
`int getchar(void)`	Reads a single character from `stdin`.
`int puts(const char *str)`	Writes a string followed by a newline to `stdout`.
`char gets(char str)`	Reads a string from `stdin` (unsafe, use `fgets()` instead).
`char fgets(char str, int n, FILE *stream)`	Reads a string from `stream` with buffer overflow protection.
`int fputs(const char str, FILE stream)`	Writes a string to `stream`.