2.2.1 programming techniques

sequence

code is executed line-by-line, from top to bottom

branching

• a certain block of code is run if a specific condition is met, using IF statements

• also known as ‘selection

iteration

• a block of code is executed a certain number of times or while a condition is met

• Iteration uses FOR or WHILE loops

  • count-controlled Iteration is repeated a given number of times

    • for i in range (0,10): 

    • print i

  • condition-controlled Iteration continues until a given condition is met

    • while i <= 20: 

    • print “Not true”; 

    • i=i+1 

    • endwhile  

recursion

• a programming construct in which a subroutine calls itself during its execution

• this continues until a certain condition - called the stopping condition / base case - is met, at which point the recursion stops

ADV recursion

• represented in fewer lines of code, which makes them less prone to errors

• however it is essential that recursive subroutines are clearly defined so as to reach a stopping condition after a finite number of function calls

DIS recursion

• inefficient use of memory

  • if the subroutine calls itself too many times, there is a danger of a stack overflow, which is when the call stack runs out of memory

  • this would cause the program to crash

• recursion is difficult to trace, especially with more and more function calls

local variables

• they can only be accessed within the block of code in which they were defined

• if a local variable is defined within a subroutine, it can only be accessed within that subroutine

• ensures subroutines are self-contained, with no danger of variables being affected by code outside of the subroutine

• destroyed when the subroutine exits

global variables

• global variables can be accessed across the whole program

• all variables used in the main body of a program are automatically declared to be global

• useful for values that need to be used by multiple parts of the program

• as global variables are not deleted until the program terminates, they require more memory than local variables which are deleted once the subroutine has been completed

modular programming

• technique used to split large, complex programs into smaller, self-contained modules

• a modular design also makes it easier to divide tasks between a team and manage, whilst simplifying the process of testing and maintenance, as each component can be dealt with individually

• improves the reusability of components, as once a module has been tested, it can be reused with confidence

modular programming - top down approach

• problem is continually broken down into sub-problems, until each can be represented as an individual, self-contained blackbox which performs a certain task

• also known as stepwise refinement

• these modules form blocks of code called subroutines, which can be categorised as either functions or procedures

procedures

• a self contained block of code that preforms a specific task

• doesn’t have to return a value

• can return multiple values

• typically given data as parameters for manipulation

functions

• self contained block of code that preforms a specific task

• must always return a value

• must return a single value

• makes use of local variables

parameter

variable inside the implementation of the subroutine

passing by value

• the value created for the subroutine is a copy of the original

• once it is passed in, the parameter is held in a separate memory location

  • therefore is only available to that subroutine

• the copy is now a local variable of that subroutine

  • its value outside the subroutine will not be affected

passing by reference

• a pointer that contains the memory address of the original value is created

• any changes to that value from within the called subroutine will also affect the value of the original variable

IDE def

• Integrated Development Environment

• a program which provides a set of tools to make it easier for programmers to write, develop and debug code

features of an IDE

• stepping

  • allows you to monitor the effect of each individual line of code by executing a single line at a time

• variable watch

  • sometimes used to pinpoint errors, this is a useful feature to observe how the contents of a variable change in real-time through the execution of a program

• breakpoint

  • allow users to set a point in the program at which the program will stop.

  • can either be based on a condition or set to occur at a specific line.

  • help to pinpoint where an error is occurring

• debugging

  • tools Some IDEs also provide run-time detection of errors with a guide as to where in the code they are likely to have occurred through line numbers and highlighting

• auto complete

  • start typing a command and it fills in the rest

• auto indent

  • indents code automatically within structures to avoid errors

class

• a template for objects

• defines a data structure by providing initial values for attributes and methods

attribute

characteristics of a class that can be accessed by other objects

method

• a function that is defined inside a class and typically operates on objects of that class

• used to manipulate the attributes of an object and perform operations on it

object

an instance of a class

encapsulation

bundling of data with the methods that operate on the data

ADV of reusable components

• saves time from having to write the same algorithm again

• reduced testing requirements

aggregation

relationship between two classes where one class contains or is composed of one or more objects from another class

composition

• implements a has-a relationship between classes

• one class contains 1 or more objects from another class

polymorphism

allows you to work with objects of different types though a common interface

inheritance

• capability to derive a class properties and characteristics from another class

• implements an is-a relationship between classers

constructor

creates an instance of an object from a class

operators

=,+=,<,>

use of validation

check to ensure that data entered is sensible and feasible

variable

something that can hold a value

branching

allow the flow of execution to jump to a different part of the program if a specific condition is met

procedural programming

statements are executed in the order they are written

object orientated programming

• designed around objects rather than functions

• objects represent real-world entities and have attributes (data) and behaviours (methods)

• promotes modularity, code reuse, and scalability

variable

• Name (Identifier) – A unique name assigned to the variable e.g. user_age

• Data Type – Specifies what kind of value the variable can hold e.g. boolean

• Value – The actual data stored in the variable, which can change during execution

• Memory Location – The address in memory where the variable’s value is stored

• Scope – Defines where in the program the variable can be accessed e.g. local, global

instantiation

the process of creating an object (or instance) from a class