2.2.1 Programming Techniques

Code is executed line-by-line, from top-to-bottom.

When instructions/code are executed repeatedly.

Condition-controlled is when a group of instructions is repeated until a given condition is met. e.g. while, do while and repeat until loops

When a group of instructions is repeated a specific number of times. e.g. for and for each loops

Also called selection. When instructions/code are only executed if a certain condition is met.

Through IF, ELSEIF and ELSE statements and case statement

A recursive function calls itself. Each call will create a new copy of the values in the function and add all of the values of the copy the call is being made from to a stack. It has a base case (condition) that stops the recursive call, and can have multiple base cases.

Recursion is utilised when a function contains an if statement in which each if/else is followed by returning data e.g. function factorial(number) if number == 0 or 1: return 1 else: return number * factorial(number - 1); endif end function

• Recursion uses more memory / iteration uses less memory • Recursion can run out of memory / iteration cannot run out of memory • Recursion declares new variables / iteration reuses the same variables • Recursion can express a problem in fewer lines of code / iteration can take more lines of code • Recursion will call itself / iteration doesn’t

A named memory address that holds a value of a given data type. A variable can change as the program is running. A constant can not change while the program is running.

Local variables​ have limited scope which means that they can only be​ ​accessed within the block of code in which they were defined​.

• Less memory is used • Self-contained so unaffected by code outside of the subroutine • Take precedence over global variables with the same name • Increases data integrity

• Cannot be accessed directly by other subroutines • It has to be passed into a subroutine as a parameter

Global variables can be accessed from anywhere in the / across the whole program.

• Value doesn’t need passing as a parameter • Don’t need to return a value • Can be accessed from anywhere in the program • Persistent, maintaining their values throughout execution, making them suited to some constants

• Reduces data integrity as changing a global variable may have an impact on another module • Uses more memory because the memory space is declared when the program starts and remains in use throughout • Makes testing / debugging more difficult as it’s difficult to test an individual block of code

Modular programming is a programming technique used to ​split large, complex programs into smaller, self-contained modules​.

Procedures and functions are both ​named blocks of code that perform a specific task. While​ procedures do not have to return a value​,​ functions must always return a value​.

• Procedures can return multiple values whereas a function must return one, single value

A parameter is a piece of data that is input into a code block so that it can complete its task. Parameters are the variables that are called from the main body of the program to be used in a subroutine. They are written in brackets.

Arguments are the value of a parameter

When a parameter is passed by value, it is effectively treated as a ​local variable​; a ​copy of the value​ ​is passed to the subroutine and discarded at the end therefore its value outside of the subroutine will not be affected.

When a value is passed through a subroutine, the subroutine receives the memory location of where the data is stored, allowing it to be directly modified.

• The original value isn’t changed, allowing it to continue to be utilised. • Retaining the original data preserves data integrity, and prevents changes made to the parameter leading to side effects throughout the program • Suitable for small data structures • Enhances function reusability as the function doesn’t unexpectedly affect data • Easy to implement and understand, while passing by reference requires careful handling to prevent unintended changes