Standard library header <cctype>
From cppreference.com
                    
                                        
                    
                    
                                                            
                    This header was originally in the C standard library as <ctype.h>.
This header is part of the null-terminated byte strings library.
 Functions | |
|    checks if a character is alphanumeric  (function)  | |
|    checks if a character is alphabetic  (function)  | |
|    checks if a character is lowercase  (function)  | |
|    checks if a character is an uppercase character  (function)  | |
|    checks if a character is a digit  (function)  | |
|    checks if a character is a hexadecimal character  (function)  | |
|    checks if a character is a control character  (function)  | |
|    checks if a character is a graphical character  (function)  | |
|    checks if a character is a space character  (function)  | |
|    (C++11)  | 
   checks if a character is a blank character   (function)  | 
|    checks if a character is a printing character  (function)  | |
|    checks if a character is a punctuation character  (function)  | |
|    converts a character to lowercase  (function)  | |
|    converts a character to uppercase  (function)  | |