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'

Lessons in this unit:

0:	Introduction
1:	Input and output
2:	Variable scope
3:	Static variables
4:	Global variables
5:	Type definitions
6:	Enumerations
7:	Structures
8:	Command line parameters
9:	Header files
10:	The preprocessor
11:	NULL values
12:	Boolean values
13:	Nesting functions
14:	Conversion specifiers
15:	Using quotes
16:	String length
17:	Returning strings
18:	Array length
19:	Looping through arrays
20:	▶︎ Checking character values
21:	Printing percentage signs
22:	Troubleshooting: Implicit function declarations