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GCSE Computer Science UNIT 2 quiz_00005 (2.2 Programming Techniques…

- - - - Linear Search
        
        Works on un-ordered lists
        
        Compare search to list[0]. If match return 0 else compare to list[1]. If not found in list at all return -1
        
        Usually slower, but easy to code
      - Binary Search
        
        Only works on ordered lists
        
        Compare search to middle item in list. If match, stop. Else discard the upper or lower portion of the list and repeat
        
        Usually faster, but harder to code
    - - Bubble Sort
        
        incremental approach: simple to understand
        
        Compares list[0] with list[1] - swaps them if out of order. Then compares list[1] with list[2]. Repeats until first pass has been completed. Then does repeated passes until no swaps are required - list is now sorted
        
        Slow for medium/long lists (but quick to check if list is already sorted)
      - Insertion Sort
        
        Compare list(n) with all items that come before it and insert it into the correct position. Repeat for list(n+1).
        
        Quicker than a bubble sort, but still slow for very long lists
        
        Incremental approach: simple to understand
      - Merge Sort
        
        Divide and conquer approach, harder to understand
        
        Place each item into its own individual list. Each pair of adjacent lists are combined into one sorted list. Repeat until there is one big final, sorted list.
        
        Vert fast for really long lists. Other algorithms possibly faster for very short lists
        
        Much more memory intensive and difficult to code
  - - - Know the correct symbols!
- - - - print(string): outputs to string
      - Concatenation: joins two or more string together
      - string.length: returns the number of chars in the string
      - string.ToUpper and string.ToLower: converts to upper and lower case letters
      - string.substring(6,3): returns a portion of a string starting at the 7th char for 3 chars
      - string.IndexOf(substring): searches a string to find the location of a substring
      - string.Replace(x,y): replaces all occurrences of x in a string with y
      - string.Trim: removes all leading and trailing whitespace from a string
  - - - Reading a file
        
        Check file exists
        
        Open file for reading
        
        Start at line 1
        
        While not at the end of file
        
        Read each line in turn
        
        Close the file
      - Writing to a file
        
        Open file in one of two modes (if file doesn't exist it will be created)
        
        2a. If write mode then write line removes any existing data in file
        
        2b. If append mode then write line add new data to the end of the file
        
        Close the file
    - - Table: something in the real world we want to store data about e.g. cars
      - Field (column of the table): a single aspect of what we want to store data about e.g. colour of car, age of car or engine size of car etc
      - Primary key: a field in the table which acts like an index. it must be unique for every record stored. Usually some sort of ID number
      - Record (row of the table): a complete collection of data about a single individual e.g. car1, red; 1999, 2.8cc, WP50 7LW
      - Relational database: more than one table that is linked in some way. e.g. the cars table might be linked to a speeding fines table by the field 'reg plate'.
      - Structured Query Language (SQL): is the standard language for manipulating data in a database.
        
        Select all records and fields from a database
        SELECT * FROM table;
        
        Select all records from the first two fields
        SELECT field1, field2 FROM table;
        
        Select all records where engine size is greater than 2.0
        SELECT car, model, make FROM carstable WHERE engine > 2;
        
        Select all users in table where surname is smith
        SELECT forename, surname FROM users WHERE surname = "smith";
        
        Select all animals in the zoo whoes name starts with g
        SELECT * FROM zoo WHERE name LIKE "g%";
        
        Add a new record to the customers table
        INSERT INTO Customers (Name, Age, Country)
        VALUES ("Cardinal", 46, "Norway");
        note that numbers do not have quote marks around them
        
        Create a new table in the database
        CREATE TABLE employee (name text(15), age number(3), address text(30));
- - - - Limit number of logon attempts
      - Two-factor authentication
  - - - You have not followed the
        rules of the language
      - Program will not compile/run
      - Usually detected during development
      - e.g file.open() used but the correct
        syntax is file.openRead()
      - e.g. Print("hello") used but
        WriteLine("hello") is the correct syntax
      - e.g. You have used a variable
        without declaring it
      - e.g. you have missed some brackets
        or added too many brackets
      - e.g. you have used an IF
        without the corresponding END IF
      - e.g. you have made a spelling mistake
    - - You have used incorrect mathematical formula
        e.g. area of triangle = w * h
      - Correct series of instructions but in wrong order
        e.g. open file, close file, write to file
      - Incorrect conditions used
        e.g. you want red BMW's and use:
        WHERE model = 'BMW' OR colour = 'red';
      - Usually detected during testing
    - - Your program attempts something impossible
        causing it to crash when it runs
      - Usually detected during testing
      - e.g. Try to read a file that doesn't exist
      - e.g. Divide a number by zero
      - e.g. calculate the square route of a negative number
      - e.g. working with a number that is too big (overflow)
  - - - Test with valid data
      - Test with valid but extreme data
      - Test with invalid data
      - Test with null values
    - - Functional - does it work?
      - Parametric - test each subroutine separately
      - Integration - check all subroutines
        work when pout together
      - Iterative testing - test as you develop
        check all possible routes through branching code
      - User acceptance testing - fully tested by
        clients in client environment - code not considered.
      - ALPHA - Testing carried out by a small group
        within a company. Bugs reported to developers
      - BETA - Testing done outside the company by potential users
        Bugs reported to developers who fix before final software release
    - - A document with the results of all testing
      - Ensure that a program is fully tested
      - Shows test data with expected
        outcome and actual outcome
      - Code is altered if expected and
        actual outcomes are different
      - Tests that fail repeated after code
        changes to ensure that they now pass
- - - - Remember...
        1+1=10 (carry 1 and use 0)
        1+1+1 =11 (carry 1 and use 1)
  - - - e.g. 1100
        
        From right to left
        10=0
        20=0
        41=4
        81=8
        0+0+4+8=12
    - - e.g. 97
        
        97 / 2 = 48 r1
        48 / 2 = 24 r0
        24 / 2 = 12 r0
        12 / 2 = 6 r0
        6 / 2 = 3 r0
        3 / 2 = 1 r1
        1 / 2 = 0 r1
        Read from bottom to top!
        e.g. 1100001
        or in 8 bits: 01100001
      - e.g. 7
        
        7 / 2 = 3 r1
        3 / 2 = 1 r1
        1 / 2 = 0 r1
        Ans: 00000111
  - - - ASCII is a character set.
        Each char has a binary code called a code point
        e.g. "A" = 0100001
        ASCII uses 7 bits (8th bit is always 0) so there is
        not enough code points for all chars in all languages
      - UNICODE is another character set. It uses 16 bits
        for each code point so has enough for all chars in all languages
      - Extended ASCII uses the 8th bit
        and so can represent an extra 128 chars
  - - - Some data is removed from the file
        This allows for very high compression rates
        But big reduction in quality and you can
        not get the discarded data back
        Good for e.g. video, images
    - - Run length encoding
        runs of repeated chars replaced
        e.g. 0111111000001111 changed to...
        0615041
      - Dictionary encoding
        repeated words replaced by symbols
        e.g. to be or not to be changed to...
        @ { or not @ {