Check out http://www.asciitable.com/

The full list of ASCII characters are there. The function isprint() knows which of the characters are printable. isprint() returns a nonzero value if the input is a printable character, including the space character (0x20 – 0x7E). The other characters are either extended, or do other features which aren't print friendly.

More information on isprint()
isprint() is included in the ctype library, ctype.h:

int isprint(int c);
» This function returns nonzero if c is a space or a character for which either isalnum() or ispunct() returns nonzero.

int isalnum(int c);
» This function returns nonzero if c is any of or other locale-specific alphabetic character.

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According to AsciiTable.com
 Characters	ASCII
 a thru z	97 thru 122
 A thru Z	65 thru 90
 0 thru 9	48 thru 57

According to AsciiTable.com Characters ASCII a thru z 97 thru 122 A thru Z 65 thru 90 0 thru 9 48 thru 57

int ispunct(int c);
» This function returns nonzero if c is any of the following or other implementation-defined punctuation character:

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According to AsciiTable.com
 Characters			ASCII
 ! " # $ % & ' ( ) * + , - . /	33 thru 47
 : ; < = > ? @			58 thru 64
 [ \ ] ^ _ '			91 thru 96
 { | } ~				123 thru 126

According to AsciiTable.com Characters ASCII ! " # $ % & ' ( ) * + , - . / 33 thru 47 : ; < = > ? @ 58 thru 64 [ \ ] ^ _ ' 91 thru 96 { | } ~ 123 thru 126

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