ASCII Encoding, Store English To Computer

As we have mentioned before, the computer stores data in binary form. It only recognizes two numbers, 0 and 1. The text we see on the screen is converted into binary (0 and 1 sequence) before storage. ), and also find the corresponding character according to binary when displaying.

It is conceivable that a specific text must correspond to a fixed binary, otherwise confusion will occur during conversion. So, how do you map text to binary? This requires a set of specifications that computer companies and software developers must abide by. Such a set of specifications is called Character Set or Character Encoding.
Strictly speaking, character set and character encoding are not the same concept. Character set defines the correspondence between text and binary, assigns unique numbers to characters, and character encoding specifies how to store text numbers in the computer. We will not discuss these details for the time being, and consider them as one concept. In this section, I also use these two concepts interchangeably without making a distinction. The character set assigns a unique number to each character, similar to a student's student number, and the corresponding character can be found through the number.

The character set can be understood as a large table, which lists the correspondence between all characters and binary. The computer displays text or stores text, which is a process of looking up the table.

In the process of the gradual development of computers, dozens or even hundreds of character sets have appeared successively, some of which are still in use, and some have been submerged in the long river of history. In this section, we will explain a special character set for English. set - ASCII encoding.

Latin alphabet

Before we formally introduce the ASCII encoding, let's talk about what the Latin alphabet is. It is estimated that many readers, like me, are not very clear about the relationship between the Latin alphabet, the English alphabet and the letters in Chinese Pinyin.

The Latin alphabet, also called the Roman alphabet, is derived from the Greek alphabet and is the most widely used alphabet in the world today. The basic Latin alphabet is the 26 English letters such as ABCD that we often see. The Latin alphabet, the Arabic alphabet, and the Cyrillic alphabet (Cyrillic alphabet) are known as the three major alphabetic systems in the world. The Latin alphabet was originally used by Europeans. Later, due to European colonialism, this alphabet became popular around the world. The Americas, Africa, Australia, and Asia have not escaped the influence of Western culture. The same is true in China. The pinyin we use now is actually the Latin alphabet, which is an out-and-out imported product.

Later, many countries expanded the 26 basic Latin alphabets to suit their local language and culture. The most common way to expand is to add diacritics, such as ü in Chinese Pinyin, which is derived from adding two small dots on the basis of u ; another example, áà is to mark the tones on top of a.

In summary:

The basic Latin alphabet is the 26 English letters;
The extended Latin alphabet is derived from the basic 26 English letters by adding diacritics, horizontal lines, slashes, etc., and each country is different.

ASCII encoding

Computers were invented by Americans, and the first question they had to consider was how to correspond binary and English letters (that is, Latin).

At that time, various manufacturers or companies had their own practices, and the coding rules were not uniform, which brought a lot of trouble to the data exchange between different computers. But relatively speaking, there are EBCDIC invented by IBM and ASCII which can be generally recognized.

Let's start with ASCII. ASCII is short for "American Standard Code for Information Interchange".
The standard version of ASCII was first released in 1967, and the last update was in 1986. So far, a total of 128 characters have been included, including the basic Latin alphabet (English alphabet), Arabic numerals (that is, 1234567890), punctuation symbols ( ,.! , etc.), special symbols ( @#$%^& , etc.), and some characters with control functions (often not displayed).

In ASCII encoding, uppercase letters, lowercase letters and Arabic numerals are all continuously distributed (see the table below), which brings great convenience to programming. For example, to judge whether a character is an uppercase letter, you can judge whether the ASCII code value of the character is in the range of 65~90.

EBCDIC encoding is just the opposite. Its English letters are not arranged continuously, and there are many interruptions in the middle, which brings some difficulties to programming. Now even IBM itself doesn't use EBCDIC, in favor of the better ASCII.

ASCII encoding has become a universal standard for computers, no one uses EBCDIC encoding anymore, it has disappeared in the long river of history.

ASCII code list

The standard ASCII code contains a total of 128 characters, including 33 control characters (characters that have some special functions but cannot be displayed) and 95 displayable characters.

List of ASCII codes (control characters on a light yellow background and displayable characters on a white background)
binary	decimal	hex	character/abbreviation	explain
00000000	0	00	NUL (NULL)	null character
00000001	1	01	SOH (Start Of Headling)	title starts
00000010	2	02	STX (Start Of Text)	text begins
00000011	3	03	ETX (End Of Text)	end of text
00000100	4	04	EOT (End Of Transmission)	end of transmission
00000101	5	05	ENQ (Enquiry)	ask
00000110	6	06	ACK (Acknowledge)	respond/respond/receive notification
00000111	7	07	BEL (Bell)	bell
00001000	8	08	BS (Backspace)	backspace
00001001	9	09	HT (Horizontal Tab)	horizontal tab
00001010	10	0A	LF/NL(Line Feed/New Line)	newline key
00001011	11	0B	VT (Vertical Tab)	vertical tab
00001100	12	0C	FF/NP (Form Feed/New Page)	form key
00001101	13	0D	CR (Carriage Return)	enter
00001110	14	0E	SO (Shift Out)	no need to switch
00001111	15	0F	SI (Shift In)	Enable toggle
00010000	16	10	DLE (Data Link Escape)	data link escape
00010001	17	11	DC1/XON (Device Control 1/Transmission On)	Device Control 1/Transfer Start
00010010	18	12	DC2 (Device Control 2)	Device Control 2
00010011	19	13	DC3/XOFF (Device Control 3/Transmission Off)	Device Control 3/Transfer Interruption
00010100	20	14	DC4 (Device Control 4)	Device Control 4
00010101	twenty one	15	NAK (Negative Acknowledge)	No response/abnormal response/rejection
00010110	twenty two	16	SYN (Synchronous Idle)	Sync idle
00010111	twenty three	17	ETB (End of Transmission Block)	Transfer Block End/Block Transfer Terminated
00011000	twenty four	18	CAN (Cancel)	Cancel
00011001	25	19	EM (End of Medium)	End of media reached/Media storage full/Media interrupted
00011010	26	1A	SUB (Substitute)	Substitute/replace
00011011	27	1B	ESC (Escape)	escape/cancel
00011100	28	1C	FS (File Separator)	file separator
00011101	29	1D	GS (Group Separator)	group separator/grouping character
00011110	30	1E	RS (Record Separator)	record separator
00011111	31	1F	US (Unit Separator)	unit separator
00100000	32	20	(Space)	space
00100001	33	twenty one	!
00100010	34	twenty two	"
00100011	35	twenty three	#
00100100	36	twenty four	$
00100101	37	25	%
00100110	38	26	&
00100111	39	27	'
00101000	40	28	(
00101001	41	29	)
00101010	42	2A	*
00101011	43	2B	+
00101100	44	2C	,
00101101	45	2D	-
00101110	46	2E	.
00101111	47	2F	/
00110000	48	30	0
00110001	49	31	1
00110010	50	32	2
00110011	51	33	3
00110100	52	34	4
00110101	53	35	5
00110110	54	36	6
00110111	55	37	7
00111000	56	38	8
00111001	57	39	9
00111010	58	3A	:
00111011	59	3B	;
00111100	60	3C	<
00111101	61	3D	=
00111110	62	3E	>
00111111	63	3F	?
01000000	64	40	@
01000001	65	41	A
01000010	66	42	B
01000011	67	43	C
01000100	68	44	D
01000101	69	45	E
01000110	70	46	F
01000111	71	47	G
01001000	72	48	H
01001001	73	49	I
01001010	74	4A	J
01001011	75	4B	K
01001100	76	4C	L
01001101	77	4D	M
01001110	78	4E	N
01001111	79	4F	O
01010000	80	50	P
01010001	81	51	Q
01010010	82	52	R
01010011	83	53	S
01010100	84	54	T
01010101	85	55	U
01010110	86	56	V
01010111	87	57	W
01011000	88	58	X
01011001	89	59	Y
01011010	90	5A	Z
01011011	91	5B	[
01011100	92	5C	\
01011101	93	5D	]
01011110	94	5E	^
01011111	95	5F	_
01100000	96	60	`
01100001	97	61	a
01100010	98	62	b
01100011	99	63	c
01100100	100	64	d
01100101	101	65	e
01100110	102	66	f
01100111	103	67	g
01101000	104	68	h
01101001	105	69	i
01101010	106	6A	j
01101011	107	6B	k
01101100	108	6C	l
01101101	109	6D	m
01101110	110	6E	n
01101111	111	6F	o
01110000	112	70	p
01110001	113	71	q
01110010	114	72	r
01110011	115	73	s
01110100	116	74	t
01110101	117	75	u
01110110	118	76	v
01110111	119	77	w
01111000	120	78	x
01111001	121	79	y
01111010	122	7A	z
01111011	123	7B	{
01111100	124	7C	\|
01111101	125	7D	}
01111110	126	7E	~
01111111	127	7F	DEL (Delete)	delete

The above table lists the standard ASCII encoding, which contains a total of 128 characters, and the lower 7 bits (Bit) in a byte are enough to represent (2 ⁷ = 128), so the next bit will be free bit, it is wasted.

C program for ASCII encoding and decoding:

#include <stdio.h>

int main() {
    char character = 'A';
    int asciiValue = (int)character;

    printf("ASCII value of %c is %d\n", character, asciiValue);

    return 0;
}

Demonstrates how to obtain the ASCII value of a character.

Using ASCII characters in C strings:

#include <stdio.h>

int main() {
    char asciiString[] = "Hello";
    printf("ASCII representation: %s\n", asciiString);

    return 0;
}

Uses ASCII characters in a C string.