programming concepts

• Programming construct

  A building block of code, they are sequence, selection and iteration
• Sequence


  A programming construct where instructions follow, one after the other
• Selection

  A programming construct where the code makes a decision, and takes one of several branches, usually coded with IF-THEN-ELSE
• Iteration

  A code construct where the instructions repeat. Can be definite/count-controlled or indefinite/condition-controlled.
• Nesting

  Coding a second programming construct inside the first. You can do this with selection and iteration
• Definite

  The type of iteration that repeats instructions a set number of times, also called "count-controlled". Uses a FOR loop in most high-level languages
• Indefinite

  The type of iteration that repeats instructions a until a condition is met, also called "condition-controlled". Uses WHILE or REPEAT... UNTIL in high-level languages
• WHILE

  This statement starts a condition-controlled loop with the condition at the start, so the loop will only begin if the condition is true
• REPEAT


  A statement that starts a condition-controlled loop with the condition at the end in an UNTIL statement, it will run once even if the condition is false
• Subroutine

  A small set of instructions that completes a specific task, sometimes called a subprogram. It can be a function or procedure
• Procedure

  A subroutine which does not return a value. For example it might redraw the screen or write a record to a file
• Function

  A subroutine which returns a value. It might return a random dice roll, calculate a ticket price or determine your exam grade
• Variable

  A named memory location holding a single value that can change during the program, e.g. name, age, x, y
• Constant

  It cannot change. A named memory location for something that stays the same. Examples are PI, Number_of_Levels, MAXHEALTH
• Identifier

  The name we give to variables, constants and subroutines, it should be meaningful
• Meaningful


  All identifiers should be this, it means they are readable and reflect the values they represent. MAXLIVES, player1_score and get_health are all OK, but m, p1 and h are not
• Input

  Any data that is received into a program while it is running, we can use USERINPUT for this in AQA pseudo-code
• Output


  Information that is produced by a program and made available for us to see or hear, we use OUTPUT in AQA pseudo-code
• Assignment

  A statement that assigns a value to a variable. The right side of the equals sign can be any expression. These are valid:health ← 100fare ← 5 + 0.5 * milesdiscount ← time < 8 AND band=="Senior"