Header file: #include <cctype>
1. The following functions are used to determine letters:
- std:: isspace ('0');//Whether it is a blank character (space, horizontal tab character'\t', vertical tab character'\v', line feed character'\n', page feed character'\f' , Carriage return character'\r')
- std:: isalpha ('0');//whether it is a letter (not including the underscore'_')
- std:: isdigit ('0');//Whether it is a decimal number ('0'~'9')
- std:: isxdigit ('0');//Whether it is a hexadecimal number ('0'~'9','a'~'f','A'~'F')
- std:: isupper ('0');//whether uppercase letters
- std:: islower ('0');//whether lowercase letters
- std:: isalnum ('0');//Is it a letter or number
- std:: iscntrl ('0');//Whether to control characters (ASCII 0~31, 127)
- std:: ispunct ('0');//whether letters, numbers, blanks, visible control characters
- std:: isgraph ('0');//Whether letters, numbers, visible control characters (excluding white space)
- std:: isprint ('0');//Whether the displayed characters can be printed
2. Letter case
- std:: toupper gets the uppercase of letters
- std:: tolower gets lowercase letters