Computer Science - 2B Programming Techniques

Subroutine

giving an identifier to a block of code. Allows us to reuse that code throughout the program

Procedure

just executes code without returning a value

Function

executes code and returns a value

Parameters

data fed into a subroutine to be used within its code. Defined in the brackets after the subroutine's identifier

Return

returns a value from a subroutine

Why use subroutines? [5]

- modularised approach breaks down programs into manageable chunks of code
- helps to decompose larger problems
- programmers only need to use the interfaces of subroutines, i.e. parameters and return values
- don't need to worry about internal workings
- programs will have fewer bugs as we use structured programming techniques

Local variable

only exist inside the structure they are defined in (I.e. subroutine, while loop, if statement etc.)

Global variable

exist everywhere in the code. Must be defined outside of any structures (I.e. not indented)

Scope

the part of a program where a variable is visible and can be used by the code.

Advantage of using local variables:

keep a subroutine self-contained for use in any program, so variable names will not conflict

Structured programming techniques

techniques consisting of top-down program design, pseudocode, flowcharts, and logic structures

Data validation

ensuring that users enter the correct data type

Different validation routines [5]:

- range check
- type check
- length check
- presence check
- format check

range check

ensures a field is between a certain range of values.

type check

data is of the right type, such as integer, letter or text

length check

checks data is correct length

presence check

requires a field to be completed.

format check

checks the data is in the right format

Data verification

double-check that data has been typed in correctly

Authentication routines

used to make sure a person is who they claim to be

Examples of authentication routines [3]:

- ask for user ID and password
- biometrics
- reCAPTCHA

Maintainable code [5]:

- comments at the top for who wrote the program and when
- comments to explain complex code
- subroutines have comments to explain their use
- meaningful variable names
- modular structure

Trace table

a table that follows the values of variables to check for accuracy/function of program

What is a trace table useful for? [3]

- determining the purpose of an algorithm
- finding the output of an algorithm
- finding errors in an algorithm

Logic error

a mistake in the algorithm or program that causes it to behave incorrectly or unexpectedly

Syntax error

an error in a program that makes it impossible to parse — and therefore impossible to interpret

What types of test data are there? [3]

- normal data
- boundary data
- erroneous data

Normal data

entering data that should be acceptable to the solution

Boundary data

data either side of the range extremes

Erroneous data

test data that a program isn't designed to accept