2.2 Programming V2

2.2 Programming V2

1. Subroutines

   • Procedures
     • Are defined and called by their names
     • They do not return their values
   • Functions
     • Are called by assigning their return value to something
     • They always return a single value
   • Defines a large amount of coding into one value
     • Useful to reuse code faster
     • Good so work can be split between programmers
       • Variables
         • Values change throughout the program
       • Constants
         • Stays fixed throughout the program
       • Used within subroutines
         • Both are used to store data whilst the program is running

2. SQL (Standard Query Language)

   • Programming language used to work with databases
   • Can be run from a special window in a database package
   • SQL Keywords
     • SELECT
       • The variable you want to find
     • FROM
       • From which database
         • e.g. To find a SongTitle more than 3 mins long
           • SELECT SongTitle FROM Songs WHERE Length > 3
     • WHERE
       • Different columns

3. Iteration

   • The repetition of a process
   • For Counter (Counter-controlled)
     • Loops for a specific number of times, depending on the counter number
   • While Loop (Condition-controlled)
     • Better for user interfaces
     • Loops until the condition is met/changes

4. Operators

   • Arithmetic Operators
     • / - Division
     • * - Multiplication
     • + - Addition
     • - - Subtraction
     • MOD - Modulus (Remainder) e.g.12 MOD 5 = 2
     • DIV - Ouotient e.g. 17 DIV 5 = 3
     • ^ - Exponentiation (To the power of)
   • Represents the operations that are performed on the data
   • String Operators (String Manipulation)
     • .length - Number of characters in a string (including spaces)
     • .lower - lowercase
     • .upper - UPPERCASE
     • .substring (x,y) - Part of a string
   • Comparison Operators
     • != - Not equal to
     • == - Equal to
     • < - Less than
     • > - Greater than
     • <= - Less than or equal to
     • >= - Greater than or equal to
   • Logical Operators (Only used in Booleans)
     • AND - Two conditions must be met for the statement to be true
     • OR - At least one condition must be met for the statement to be true
     • NOT - Inverts the results e.g. NOT(A and B) will only be false when both A and B are true`

5. Arrays

   • Begins with 0
   • Usually have fixed sizes and occupy a fixed (static) amount of memory
   • A table of organised data
   • Advantages
     • Non-sequential nature - can jump between non-neighbouring elements instantly without having to browse through the whole array
     • Good for ease of iterating through an array - allows us to manipulate multiple times of data with very few lines of code,replacing may separate variables
   • 2D Arrays
     • Has rows and columns
     • Each individual rows/columns/index hold different series of data
   • 1D Array
     • Only holds one series of data (like a pie chart)

6. Selection

   • Allows a computer to "think" - make decisions
   • Changes the flow of a program, depending on a set of conditions, it is used for validation, calculation and making sense of a user's choices
     • e.g. IF, ELIF, ELSE, SELECT CASE statements
   • Nested Selection
     • Sometimes, we can only evaluate a condition if some pre-condition is met. We would need two selection statements, one inside the other
     • The "outside" selection is the pre-condition, while the "inside" selection is the conditon
     • e.g. IF....... IF
       • IF Statement within an IF Statement

7. Sequencing

   • Allows a programmer to solve complex tasks through a number of simple instructions (sequence/algorithm)
   • Advantages
     • Each line follows the next
     • Create simple programs very quickly
     • Easy to follow for a small program
     • Fundamental priniciple of a program
     • Starts at the top, finishes at the bottom
   • Disdavantages
     • Not at all efficient
     • Extremely hard to maintain
     • Becomes very difficult to follow with large problems