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Introduction
Introduction
In short, there are two main classes of data - singular and complex. Singular data has one value for one variable .Singular data types include:
Integer - whole numbers including negative values, zero and as high or low as you want to declare. a 32-bit positive integer has a value or 4.3 billion or so.
String - text values. Names, addresses passwords are all string variables. Numeric data can be stored as a string, but leads to some interesting side effects.
Floating point, or Real - decimal or fractional numbers.
Boolean - Logical operators, True of False. This is the basis of Boolean Algebra which is used to understand the logic of how a CPU works. See Binary Arithmatic and Truth Tables for more information.
The presentation below has a lot of detail on data structures. It's made to be viewed in this page and all information is on the slides. There are no speaker notes.
Integer representation
Integer representation
Binary (base 2), decimal (base 10), hexadecimal (base 16) numbers. The presentation below is nicked from the HSC course but it gives a nice overview of the different number systems we use in human and nerd societies. Most people think and work in decimal; numbers 0-9 and so on. Computers thing in Binary; 0 and 1 and nerds tend to think in base 16, Hexadecimal.
Binary is a little clunky for people, so it is "simplified" to Hexadecimal. Hex takes four binary bits and turns them into one hex character.
Character representation in binary, decimal and hex
Character representation in binary, decimal and hex
ASCII (American Standard Code for Information Interchange), EBCDIC and others
The ASCII table and how to use it:
Every English character (and not other languages, ASCII stands for American Standard Code for Information Interchange, so was developed for the English language) can be represented in 7-bit ASCII.
Read the ASCII table as a two-dimensional grid, reading the most significant (the 7th bit) first.
Look at the Character A in the table below. Its ASCII is 100 (the 7th, 6th and 5th data bits from the table header), then 0001 for the remaining four data bits.
A = 1000001
a = 1100001
The difference is the 6th data bit. This is why user names don't need to be case sensitive and why passwords can be. That sixth data bit gets ignored or included.
What's your name in ASCII?
The control characters at the bottom of the table are communication and data transmission characters that were used in communication systems of old. (read more)
Limitations of data types
Limitations of data types
The data types presentation above has a slide discussing lmitations of data types, an extract is reproduced below.
it's about knowing what the variable will be used for and what the limitations will be.
Consequences for not knowing this can be quite extreme. Ever used an R4 card in your DS? It's based around a variable in a save file that got away from the developers' grasp which allowed a hacker to write data beyond the end of the memory allocated to the save file and into main memory.
Complex data structures - Arrays and Records
Complex data structures - Arrays and Records
complex in the sense that they hold many values of one type (array) and many values of many types (records). The presentation above discusses complex data structures in detail.
a data dictionary to define data in a solution
a data dictionary to define data in a solution
a data dictionary defines the structure of data, key properties and uses of variables and objects and where they are to be used in the system or solution.
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