U7

• Sequence

  Structuring code into a logical, sequential order
• Selection

  Decision making using if statements
• Iteration

  Repeating code using for or while loops
• Variables


  Used to store data in programs, can be changed as the program runs
• Variable

  Has two parts - the data value and an identifier
• Efficient program

  • Uses variables with sensible identifiers that immediately state their purpose in the program
• Local variables


  Declared within a specific subroutine, can only be used within that subroutine
• Global variables


  Can be used at any point within the whole program
• Local variable advantages

  • Saves memory, easier to debug, can reuse subroutines in other programs
• Global variable advantages

  • Variables can be used anywhere in the whole program, makes maintenance easier, can be used for constants
• Constant

  Data that does not change in value as the program is run, it is fixed and remains the same
• Comparison operators


  Used to compare two data values
• Common comparison operators

  • Equal to
  • Not equal to
  • Greater than
  • Less than
  • Greater than or equal to
  • Less than or equal to
• Arithmetic operators


  Used to mathematically manipulate values
• Common arithmetic operators

  • Add (+)
  • Subtract (-)
  • Multiply (*)
  • Divide (/)
  • Modulo division (%)
  • Integer division (//)
  • Exponentiation (^)
• Logical operators


  Typically use TRUE and FALSE values (Boolean)
• An array is a static data structure that can hold a fixed number of data elements. Each data element must be of the same data type i.e. real, integer, string.
• Index

  The number that indicates the position of a data element in an array. The first element in an array always has an index of 0.
• Traversing an array

  Use a for loop to display each data element in order
• Inserting a value in an array

  Change the value of elements that already exist (cannot insert new values)
• Deleting a value in an array


  Overwrite the element with a blank space (cannot delete values)
• Searching an array

  Use a for loop to search through each element for a specific value
• Two-dimensional array

  An array with multiple rows and columns, where the data must still be of the same data type
• Printing a specific data element in a two-dimensional array

  Use the index number for the row and column
• Searching a two-dimensional array

  Use two for loops, one for the rows and one for the values in each row
• Record

  Can store data of different data types, each record is made up of information about one person or thing, each piece of information is called a field, records should have a key field that uniquely identifies each record
• SQL (Structured Query Language)

  A language used to search for data in a database, the format is:

  SELECT field1, field2, field3...

  FROM table

  WHERE criteria
• SQL uses wildcards, which are symbols used to substitute characters. The * symbol represents ALL fields.
• Programs create and process data, which is stored in files that can be accessed, changed and shared
• Data types


  • Character
  • String
  • Integer
  • Real
  • Boolean
• Creating a new file in Python

  1. Open file for writing using the open() function with the "w" parameter

  2. Specify the name of the file (e.g. "users.csv")
• Character


  A single character, such as a letter, number or punctuation symbol
• Opening a file in Python

  1. Use an open command to open the file

  2. The variable holds a pointer to the file once it is opened, it's called the file object or file handle
• String


  A sequence of characters, including letters, numbers and punctuation
• If you don't specify a flag, the file is opened read-only
• Reading a file in Python

  1. Open the file

  2. Use the readline() method to read one line at a time from the start of the file

  3. Close the file using the close() command
• Integer


  A whole number
• Reading an entire file into a list in Python


  1. Open the file

  2. Use the readlines() method to read the whole file into a list

  3. Close the file using the close() command
• Real


  A decimal number
• Boolean


  An answer that only has two possible values