programming concepts

• a variable is a location in memory which stores a value that can be changed
• a constant is a location in memory which stores a value that does not change
• reasons for using a constant:

  • only have to change the value once in the source code
  • makes sure the program is consistent as only have to enter the value once
  • makes code more readable
• sequence 


  the idea of one step being done after another in a particular order
• iteration

  repeating sections of code in a loop (for, while, repeat)
• selection

  changing the direction of a program based on a specific criteria (if, elif, else)
• if you don't know how many times a loop will repeat, you use an indefinite loop / condition-controlled loop
• two types of indefinite loops

  • pre-controlled loops
  • post-controlled loops
• pre-controlled loops

  the condition is checked before the loop starts and will keep going whilst the condition is true
• post-controlled loops

  the condition is checked once the loop has finished and will stop as soon as the condition is true
• if you do know how many times the loop will repeat, you use a definite loop / counter-controlled loop
• nested loops

  putting loops inside each other
• nested if statements

  if statements within each other
• relational operators

  being able to compare two values and return either true or false
• <

  less than
• >

  greater than
• =

  equals
• !=

  not equal
• <=

  less than or equal to
• >=

  greater than or equal to
• arithmetic operators

  mathematical calculations within in a program
• +

  addition
• -


  subtraction
• *


  multiplication
• /

  division
• MOD

  finds the remainder when the first number is being divided by the second
• DIV

  finds the whole part when the first number is being divided by the second
• boolean operators

  being able to compare one or two boolean values and return either true or false
• not

  reverses the input (not true = false)
• and

  checks if both inputs are true and returns true if so, false otherwise
• or

  checks if either input is true and returns true if so, false otherwise