Computer science

• Variable


  • Space in memory large enough to hold a single piece of data
  • Each variable has a name and data type – name chosen by programmer
  • Should not be reserved keywords, begin with letter, no spaces, differs from programming language
• Data type


  Kind of data that can be stored in the variable – yes/no, true false, letters, numbers – automatically decided in python and java script
• Constants


  Similar to variable – difference is that once it has been given a value it can not be changed – value cant change
• Assignment


  Storing a value, placing a value into the variable or constant
• Variable more commonly used – constants better because it cant be accidentally changed – VAT, pi would be constants since their value doesn't change
• Sequence


  When an instruction is executed once, never any variation – used when programmer wants the same results each time – basic operations performed on a calculator
• Selection


  Execution can follow two or more paths – e.g. adult, child, time of day, size of group – spotted by keywords – if, else, select, case, selection box
• Iteration


  Block of code can run more then once, rather then pasting multiple times – code is placed in loop, loops programmed repeatedly, less prone to mistakes – told to loop a fixed number of times, loops until particular task is done – search for item until it is found or until it is tired – keywords: for, while, loop, until
• Arithmetic operation


  Both the input and outputs are numbers
• Logical operation


  The output is either true or false
• You need to be able to predict outcome
• Arithmetic operations


  • + - add
  • - subtract
  • * multiplication
  • / divide
  • () exponents : 2^3
• Variables can be assigned as the result of an arithmetic operation
• Div


  Integer division – disregards remainder
• MOD


  Retains only the remainder
• Logical expressions


  • = equal to
  • < less than
  • > greater than
  • <= less than or equal to
  • >= greater than or equal to
  • != and not equal to
• AND


  Must both be true in order for the whole connected expression to be true
• OR


  If the first, second or both expressions are the whole combined expression is true
• NOT


  Simply makes that expression the opposite of what it was before
• Algorithm


  Set of instructions that a computer follows in order to complete a task or solve a problem
• Common features of algorithms


  • Variable
  • Conditionals
  • Repetition
  • Data structure
  • Subprograms
• Integer


  Store whole number – positive, negative, 0
• Real data type


  Stores numbers that can be fractions
• Boolean data types


  Only true of false, can contain no other values, useful for determining whether a loop should execute one more time if a password was correctly entered
• Character data type


  Can contain a single character – letter, one digit number, symbol – good for abbreviations
• String data type


  Can store sequence of individual characters – stores names and description, combinations of letters and numbers (postcodes), barcodes, no mathematical executions on the data
• Casting


  Take data from a variable, change data type and place it into a different variable
• String


  Sequence of characters – names, addresses, post codes, etc
• String operation


  Any process on string – calculating the string length, breaking string into pieces
• Length


  Used to find how many characters are in a string
• Index within a string


  Tell you the position of each character
• Substring


  Part of a larger string
• Array


  Can only store data of a single data type
• Records


  Can store multiple pieces of data belonging to different data types
• Field


  Each item in a record
• Database


  Structured means of storing data within a computer system
• Main advantage of a database – can look at the data in a range of different ways
• Table


  In a database, fields across the top, records down the rows
• Primary key


  Special field that uniquely identifies each record
• Open


  File must be opened before data can be read from or written to