ASCII Code

Question 1

What is the ASCII standard? (Definition)

Answer

The ASCII (American Standard Code for Information Interchange) character encoding standard is an encoding system that assigns a unique numerical code to each character (letters, numbers, symbols) on a computer, which facilitates the exchange of data between different computer systems.

This standard was defined in 1975 and contains 128 7-bit codes including 95 printable characters (i.e. the vast majority of characters allowing writing in English, but not fully in other languages, there are no accents for example).

Today this standard is outdated and supplanted by Unicode, which is backward compatible with ASCII.

Question 2

How to encode using ASCII table?

Answer

Encoding/Encryption consists of replacing/translating each character with its value in the ASCII table (see below). This value can be written in several formats, depending on the needs, such as decimal, binary, hexadecimal or even octal.

Example: Convert dCode string in ASCII, that is writing 1100100 1000011 1101111 1100100 1100101 in binary (7-bit) or 100 67 111 100 101 in decimal.

Characters which don't exist in the encoding table cannot be coded (no special characters, accents, etc.)

Question 3

How to decode/decrypt ASCII?

Answer

ASCII decoding/conversion consists of replacing/translating each value (binary, octal, decimal or hexadecimal) with the corresponding character in the ASCII table. Its representation can be independently formatted into binary (0-1), octal (0-7), decimal (0-9) or hexadecimal (0-9a-f).

Example:

ASCII Values (Format)	Texte clair
65 77 69 82 73 67 65 78 (Decimal)	AMERICAN
83 116 97 110 100 97 114 100 (Decimal)	Standard
1000011 1001111 1000100 1000101 (7-bit Binary)	CODE
01100011 01101111 01100100 01100101 (8-bit Binary)	code
49 4E 46 4F 52 4D 41 54 49 4F 4E (Hexadecimal)	INFORMATION
111 116 124 105 122 103 110 101 116 107 105 (Octal)	INTERCHANGE

Question 4

How to recognize an ASCII ciphertext?

Answer

The message is generally written either in binary, or in decimal, or in hexadecimal (or rarely in octal).

The values are between 0 and 127 (decimal), the most common/frequent, corresponding to usual characters such as uppercase or lowercase letters are between 65 and 122 (decimal).

Any reference to skiing (ASCII ≈ a ski) or sky is a clue.

Computer languages usually use functions like fromCharCode(), CharCode(), Chr()

Question 5

What are the different formats (HEX, BIN, DEC) to write in ASCII?

Answer

The ASCII table assigns a unique numeric code to each character, but this code (between 0 and 127) can be written in multiple ways depending on the needs.

— BIN: writing in binary base 2 (from 0 to 1111111)

— BIN /7: division every 7 bits (from 0000000 to 1111111)

— BIN /8: division every 8 bits (from 00000000 to 01111111)

— BIN /1-7: adaptive splitting between 1 and 7 bits

— BIN /1-8: adaptive splitting between 1 and 8 bits

— BIN /N: adaptive slicing from 1 to N bits

— OCT: writing in octal base 8 from (0 to 177)

— OCT /3: division every 3 digits (from 000 to 177)

— OCT /1-3: adaptive splitting of 1 to 3 octal digits

— OCT /N: adaptive slicing from 1 to N octal digits

— DEC: writing in decimal base 10 from (0 to 127)

— DEC /2: division every 2 digits (from 0 to 99, message without lower case)

— DEC /3: division every 3 digits (from 000 to 127)

— DEC /1-3: adaptive division of 1 to 3 digits

— DEC /N: adaptive division from 1 to N digits

— HEX: writing in base 16 hexadecimal (from 0 to 7F)

— HEX /2: division every 2 characters (from 00 to 7F)

— HEX /N: adaptive splitting from 1 to N hexadecimal digits

Numbers or characters that would not be valid in bases 2,8,10,16 are ignored.

Sometimes the symbols ⥅0 or ⥆0 are displayed, they mean that initial or final 0 have been added to allow decoding.

Question 6

How many characters is represented by an ASCII code?

Answer

An ASCII code is represented on 7 bits, which allows 128 different characters to be represented.

In practice, the ASCII code is almost always represented on 1 byte (8bits) even if it occupies only 7bits.

In binary, use either 7 bits or 8 bits (by adding a leading zero) to represent an ASCII character.

In octal, it is represented with 3 characters (from 000 to 177).

In decimal, the number is between 1 and 128 (from 1 to 3 characters).

In hexadecimal, 2 characters are used (from 00 to 7f).

Question 7

How do I change from a lowercase ASCII letter to an uppercase letter?

Answer

In the ASCII code there is a difference of 32 between an uppercase letter and a lowercase letter. So add 32 to the ASCII code of a capital letter to get a lowercase and subtract 32 from the ASCII code of a lowercase letter to have a capital letter. The corresponding binary operation consists in setting the 5th bit (starting from the right) to 0 (upper case) or 1 (lower case).

Example: A=01000001 (65) and a=01100001 (65+32=97)

This trick does not work for accented letters, which are not in the basic ASCII table

Question 8

What is the full ASCII table?

Answer

Full 7-bit ASCII table

Decimal	Octal	Hex	Binary	Character	Info
000	000	00	0000000	NUL	(Null char.)
001	001	01	0000001	SOH	(Start of Header)
002	002	02	0000010	STX	(Start of Text)
003	003	03	0000011	ETX	(End of Text)
004	004	04	0000100	EOT	(End of Transmission)
005	005	05	0000101	ENQ	(Enquiry)
006	006	06	0000110	ACK	(Acknowledgment)
007	007	07	0000111	BEL	(Bell)
008	010	08	0001000	BS	(Backspace)
009	011	09	0001001	HT	(Horizontal Tab)
010	012	0A	0001010	LF	(Line Feed)
011	013	0B	0001011	VT	(Vertical Tab)
012	014	0C	0001100	FF	(Form Feed)
013	015	0D	0001101	CR	(Carriage Return)
014	016	0E	0001110	SO	(Shift Out)
015	017	0F	0001111	SI	(Shift In)
016	020	10	0010000	DLE	(Data Link Escape)
017	021	11	0010001	DC1	(XON)(Device Control 1)
018	022	12	0010010	DC2	(Device Control 2)
019	023	13	0010011	DC3	(XOFF)(Device Control 3)
020	024	14	0010100	DC4	(Device Control 4)
021	025	15	0010101	NAK	(Negative Acknowledgement)
022	026	16	0010110	SYN	(Synchronous Idle)
023	027	17	0010111	ETB	(End of Trans. Block)
024	030	18	0011000	CAN	(Cancel)
025	031	19	0011001	EM	(End of Medium)
026	032	1A	0011010	SUB	(Substitute)
027	033	1B	0011011	ESC	(Escape)
028	034	1C	0011100	FS	(File Separator)
029	035	1D	0011101	GS	(Group Separator)
030	036	1E	0011110	RS	(Request to Send)(Record Separator)
031	037	1F	0011111	US	(Unit Separator)
032	040	20	0100000	SP	(Space)
033	041	21	0100001	!
034	042	22	0100010	"
035	043	23	0100011	#
036	044	24	0100100	$
037	045	25	0100101	%
038	046	26	0100110	&
039	047	27	0100111	'
040	050	28	0101000	(
041	051	29	0101001	)
042	052	2A	0101010	*
043	053	2B	0101011	+
044	054	2C	0101100	,
045	055	2D	0101101	-
046	056	2E	0101110	.
047	057	2F	0101111	/
048	060	30	0110000	0
049	061	31	0110001	1
050	062	32	0110010	2
051	063	33	0110011	3
052	064	34	0110100	4
053	065	35	0110101	5
054	066	36	0110110	6
055	067	37	0110111	7
056	070	38	0111000	8
057	071	39	0111001	9
058	072	3A	0111010	:
059	073	3B	0111011	;
060	074	3C	0111100	<
061	075	3D	0111101	=
062	076	3E	0111110	>
063	077	3F	0111111	?
064	100	40	1000000	@
065	101	41	1000001	A
066	102	42	1000010	B
067	103	43	1000011	C
068	104	44	1000100	D
069	105	45	1000101	E
070	106	46	1000110	F
071	107	47	1000111	G
072	110	48	1001000	H
073	111	49	1001001	I
074	112	4A	1001010	J
075	113	4B	1001011	K
076	114	4C	1001100	L
077	115	4D	1001101	M
078	116	4E	1001110	N
079	117	4F	1001111	O
080	120	50	1010000	P
081	121	51	1010001	Q
082	122	52	1010010	R
083	123	53	1010011	S
084	124	54	1010100	T
085	125	55	1010101	U
086	126	56	1010110	V
087	127	57	1010111	W
088	130	58	1011000	X
089	131	59	1011001	Y
090	132	5A	1011010	Z
091	133	5B	1011011	[
092	134	5C	1011100	\
093	135	5D	1011101	]
094	136	5E	1011110	^
095	137	5F	1011111	_
096	140	60	1100000	`
097	141	61	1100001	a
098	142	62	1100010	b
099	143	63	1100011	c
100	144	64	1100100	d
101	145	65	1100101	e
102	146	66	1100110	f
103	147	67	1100111	g
104	150	68	1101000	h
105	151	69	1101001	i
106	152	6A	1101010	j
107	153	6B	1101011	k
108	154	6C	1101100	l
109	155	6D	1101101	m
110	156	6E	1101110	n
111	157	6F	1101111	o
112	160	70	1110000	p
113	161	71	1110001	q
114	162	72	1110010	r
115	163	73	1110011	s
116	164	74	1110100	t
117	165	75	1110101	u
118	166	76	1110110	v
119	167	77	1110111	w
120	170	78	1111000	x
121	171	79	1111001	y
122	172	7A	1111010	z
123	173	7B	1111011	{
124	174	7C	1111100	\|
125	175	7D	1111101	}
126	176	7E	1111110	~
127	177	7F	1111111	DEL	(Delete)

The values from 128 to 255 do not exist in the ASCII table. There are other tables often called extended ASCII which complement the ASCII code but are not ASCII.

Question 9

How to code non-ASCII characters such as accents?

Answer

Use another coding table, such as Unicode or in Europe the norm ISO/CEI 8859-1 Latin which includes the ASCII table in its first part (from 0 to 127) then specific characters for the following numbers (128-255).

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_
1_
2_	␣	!	"	#	$	%	&	'	(	)	*	+	,	-	.	/
3_	0	1	2	3	4	5	6	7	8	9	:	;	<	=	>	?
4_	@	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O
5_	P	Q	R	S	T	U	V	W	X	Y	Z	[	\	]	^	_
6_	`	a	b	c	d	e	f	g	h	i	j	k	l	m	n	o
7_	p	q	r	s	t	u	v	w	x	y	z	{	\|	}	~
8_
9_
A_	⌴	¡	¢	£	¤	¥	¦	§	¨	©	ª	«	¬	-	®	¯
B_	°	±	²	³	´	µ	¶	·	¸	¹	º	»	¼	½	¾	¿
C_	À	Á	Â	Ã	Ä	Å	Æ	Ç	È	É	Ê	Ë	Ì	Í	Î	Ï
D_	Ð	Ñ	Ò	Ó	Ô	Õ	Ö	×	Ø	Ù	Ú	Û	Ü	Ý	Þ	ß
E_	à	á	â	ã	ä	å	æ	ç	è	é	ê	ë	ì	í	î	ï
F_	ð	ñ	ò	ó	ô	õ	ö	÷	ø	ù	ú	û	ü	ý	þ	ÿ

All non-visible characters are control characters (see ASCII table from 1 to 31)

Question 10

What is the difference between ASCII and Unicode?

Answer

The main difference between ASCII and Unicode is the range of characters they can represent. ASCII uses a character table of 128 codes, which is suitable for representing basic English characters. In contrast, Unicode is a newer standard that uses a much larger character table, allowing thousands of characters used in different languages and scripts around the world to be represented.

ASCII Code

ASCII Converter

ASCII Encoder

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