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47 lines
1.8 KiB
Markdown
47 lines
1.8 KiB
Markdown
---
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title: "characters"
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aliases:
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tags:
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- cosc204
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---
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# Characters
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- A written symbol.
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- In english are represented as a single byte, (other languages use 2 bytes or more)
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- e.g., [different types of characters](https://i.imgur.com/DBLVhw8.png)
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- characters are joined together to make human readable numbers and words
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- `char ch`
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- ch is a variable name (identifier)
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- used to label a location in the computer's memory where a byte is stored
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- when the code is compile, the name is assigned an address, in memory. The meaning of that data depends on how a human interprets it. it might be small integer, or a character, or a color etc.d
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- each byte (or group of bytes) represents a number which maps to a character using a mapping like [Unicode](notes/characters.md#Unicode) or [ASCII](notes/characters.md#ASCII)
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# ASCII
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A char is a 7-bit number (usually stored as a byte with the 8th bit set to zero) used as an index into a table of characters. The font describes how to draw these characters
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- ASCII (american standard code for information) describes what should be drawn for Roman (english like) alphabets
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- ASCII characters are stored using 7-bits
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- so there are 128 (2^7) possible characters
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- stored as a byte with the 8th bit set to zero
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- For sorting purposes characters are compared on their numeric value (called the *collating sequence*)
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- 'A' is before 'Z' but 'a' is after 'Z'!
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# Unicode
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A 21-bit code with 144,697 characters from 159 scripts
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- Other non roman languages
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- greek, arabic, chinese, hebrew, japanese, thai etc.
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- atrology symbols
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- emoji etc
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- Unicode
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- developed by the Unicode Consortium
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- coordinated with ISO/IEC 10646
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- unicode maps from character numbers (code points) into glyphs (graphical representations)
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- Some(many) are reserved |