T2B programming

What do subroutines allow?

Allows code that you intend to use multiple times to be grouped together under 1 name

Examplse of subroutines

functions and procedures

What does a function do that procedures don't?

Functions will return a value after processing has taken place

pseudocode of a subroutine

SUBROUTINE subroutineName(parameters)... ENDSUBROUTINE

why use subroutines?

Break up large programs into self-contained units

Each subroutine can be tested separately to make sure it works correctly

Cuts down development time: many programmers can work on a large program at the same time

Subroutines can be re-used in other programs

Subroutines can be stored in a subroutine library and used in different programs

Program maintenance is easier: if requirements change then just the affected subroutines need to be modified

what is the scope of a variable/constant/procedure/function?

parts of the program in which it is recognised and can be used/the specific region of a program where a variable, function, or object is visible, accessible, and can be referenced.

local variable definition

Local variable = variable created in a subroutine

local variable parameters?

Only exist while subroutine is executing, Only accessible withing the subroutine

global variable definition?

variable created outside a subroutine

'parameters' of a global variable?

accessible anywhere in the program

pseudocode of a global variable

global variablename

advantages of using local variables

Keeps a subroutine self-contained --> can be used in any program without variable names conflicting with those used in the calling program

Easier to debug program: value of that variable can only be read or changed within one subroutine

Memory efficiency: once a subroutine has finished running, the memory used for all local variables is removed

Disadvantages of using local variables

Limited scope

Potential for data redundancy (needing repeated passing)

Short lifetimes: memory freed when function ends - problematic for persistence

Advantages of Using Global Variables

Large scope: can be accessed from any function

Reduced Passing: no need to pass the same variables as parameters between different subroutines

Only needs to be declared once

Disadvantages of Using Global Variables

Harder to debug: any function can change a global variables - finding where a variables was incorrectly updated is difficult

Too many global variables can clutter namespace --> name clashes where local variable might mistakenly override a global one

Memory usage: stay in memory for entire duration of the program

What way should subroutines be written and why?

Should be written in a modular way so that they can be reused multiple times in the program or by other programs

What should well documented modules/subroutines show?

The parameters that the subroutines take, what they are used for and what data types are needed

Purpose of the subroutine

Return value and its data type

Advantages to structure programming

Modularised approach - breaks down programs into manageable chunks of code

Helps to decompose larger problems

Programmers only need to use the interfaces of subroutines = parameters and return values

Don't need to worry about internal workings of each subroutine

Fewer bugs + easier to maintain

What do data validation routines ensure?

ensure that data entered is of the right type (i.e. data type)

what can't validation make sure of?

Validation can't make sure that the user hasn't entered a wrong value/make a spelling mistake in a name

what can validation only ensure?

Can only ensure that data is reasonable and conforms to a set of rules

what is a range check?

checking data is between 2 values

what is a type check?

Data is of the right type, e.g. integer/letter/text

what is a length check?

Text entered isn't too long/short

what is a presence check?

Checks that data has been entered - field hasn't been left blank

what is a format check?

Checks that the format of, e.g., a postcode/email address is correct

what is an authentication routine

a routine to check that a user enters a valid username and password

validation definition

checking that data is reasonable

verification definition

double checking data from an alternative source or re-typing it

Ways to make Programs Easier to Understand

Comments at the top to show who wrote the program and when they wrote it

Comments to explain what harder parts of the code do

Each subroutine (function or procedure) should have comments to explain their functionality

Use meaningful variable names

Use subroutines/ a modular structure

Meaningful identifiers

What are trace tables used for?

Used to determine the outputs from a program as it runs

Enable a programmer to find errors in their programs

Can be used to find the purpose of a flowchart/pseudocode

what are syntax errors?

an error where the code written doesn't conform to the rules of the language

wat are logical errors? + description if code run

remaining error is a logical error, Program will run, but won't work as programmer intended

what is a test plan?

a structured document created during the design phase to ensure software meets requirements

what is used in normal data testing?

Uses typical/expected/valid inputs

What does normal data testing check?

Checks if a program works correctly under everyday conditions

what is used in boundary data testing?

Checks edges of valid input ranges and values just outside them (by 1)

what does boundary data testing ensure?

Ensures a program correctly accepts valid limits and rejects invalid ones, preventing errors/making software robust

what is used in erroneous data testing?

Uses incorrect/unexpected inputs (e.g. symbols, strings, negative numbers)

what does erroneous data testing ensure?

Ensures it doesn't crash + provides useful error messages, rather than processing bad data

How to find logical errors

Trace table: useful for tracing through a program in order to find a logic error

Value of each variable recorded as it changes

OUTPUT statements at various points in the program to check the values of variables