ASCII

1. Control Characters (0–31 & 127)

These characters are non-printable and used for hardware control or terminal formatting.

Dec	Hex	Oct	C Escape	Name	Description
0	00	000	\0	NUL	Null Character (String Terminator)
7	07	007	\a	BEL	Audible Bell (Alert)
8	08	010	\b	BS	Backspace
9	09	011	\t	HT	Horizontal Tab
10	0A	012	\n	LF	Line Feed (Newline)
11	0B	013	\v	VT	Vertical Tab
12	0C	014	\f	FF	Form Feed (New Page)
13	0D	015	\r	CR	Carriage Return
27	1B	033	\e*	ESC	Escape
32	20	040	(space)	SPC	Space
127	7F	177		DEL	Delete

*Note: \e is a common GCC/Clang extension but not part of the strict ANSI C standard.

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2. Printable Characters (32–126)

Commonly used characters including digits, letters, and punctuation.

Digits & Special Characters

Dec	Hex	Oct	Char		Dec	Hex	Oct	Char
48	30	060	0		33	21	041	!
49	31	061	1		34	22	042	"
50	32	062	2		35	23	043	#
51	33	063	3		36	24	044	$
52	34	064	4		38	26	046	&
57	39	071	9		61	3D	075	=

Uppercase Letters (A-Z)

Dec	Hex	Oct	Char		Dec	Hex	Oct	Char
65	41	101	A		78	4E	116	N
66	42	102	B		79	4F	117	O
67	43	103	C		...	...	...	...
71	47	107	G		90	5A	132	Z

Lowercase Letters (a-z)

Dec	Hex	Oct	Char		Dec	Hex	Oct	Char
97	61	141	a		110	6E	156	n
98	62	142	b		111	6F	157	o
99	63	143	c		...	...	...	...
103	67	147	g		122	7A	172	z

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3. Memory Aid

• Uppercase vs Lowercase: The difference between 'a' (97) and 'A' (65) is exactly 32 (or 0x20). Setting/clearing the 6th bit toggles case.
• Digit Conversion: '0' is 48 (0x30). Always use c - '0' to convert a character digit to its integer value.
• Null Pointer vs Null Char: NULL (pointer) is typically (void*)0, whereas '\0' (character) is the integer 0. They are numerically 0 but semantically different.
• Hex/Octal Limits:
  • Max 1-byte Hex: \xff (255)
  • Max 1-byte Octal: \377 (255)