How to check a character value in C

When working in C, we can use the ctype.h standard library set of functions to check the value of a char type variable.

We have access to several useful checks:

• isalnum() checks if a character is alphanumeric
• isalpha() checks if a character is alphabetic
• iscntrl() checks if a character is a control character
• isdigit() checks if a character is a digit
• isgraph() checks if a character is a printable ASCII character (but not a space)
• islower() checks if a character is lowercase
• isprint() checks if a character is a printable ASCII character
• ispunct() checks if a character is a punctuation character (a printable char, not a space, not alphanumeric)
• isspace() checks if a character is a whitespace character (see more later)
• isupper() checks if a character is uppercase
• isxdigit() checks if a character is an hexadecimal digit (0-F)

I mentioned that isspace() checks if a character is a whitespace character. What is a whitespace character?

• Horizontal tab (HT), '\t', character 9 of the ASCII table
• Vertical tab (VT), '\v', character 11 of the ASCII table
• Form Feed (FF), '\f', character 12 of the ASCII table
• Carriage Return (CR), '\r', character 13 of the ASCII table
• Space, ' ', character 32 of the ASCII table
• New line, '\n'