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Summary 2.3 - producing robust programs
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GCSE OCR COMPUTER SCIENCE J277 2.3 - producing robust programs 2.3.1 Defensive design, 2.3.2 Testing
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Defensive desigrr helps to ensure that programs are functioning properly. They should never break orproduce errors if they are functioning properly.
+ anticipate how users may misuse their program, then attempt to prevent it from happening
, ensure the code is well-maintained
) reduce the number of errors in the code throush testins
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The easiest way for misuse in a program is when enteiing data. This can be prevented using validation.
INPUTVAIIDATION-l checking if data meets certain criteria before passing it into the program
o Range check - checks the data is within a specified range --o 1,., w,f sov1 ! o.ho- -,sr.,.o.,q\ o[
. presence check - checks data has been entered u^u2a1k$ c\,r.crrq.clevS +"..) r,.,^.
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Format check - checks data has the correct format e.g. adare SOL ir,\
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. Look-up table - checks data against a table of acceptable values
r tlrpe check - checks data is the right type such as string, integer etc
o Length check - checks the data is the correct length
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AUTHENTICATION - confirms the identity of a user before they are allowed to access certain pieces of data
or features of the program. This is commonly done using passwords.
E.g. passwords, user ID, PIN number, biometric security such as facial/voice recognition, pattern recognition
To increase the securitv of Dassword -based authentication svstems:
) force users to use strong passwords and to change them regularly
-) limit the number of failed authentication attempts before access is lost
+ ask for a random selection of characters from the password on each authentication
To imDrove the main bilitv of a nrosram
) comments are useful to explain the key features of a program - they are fundamental to help other
programmers understand your program
-) indentation is used to separate different statements in a program. This allows other programmers to pick
out the different features
)identifiers should be named suitably so they refer to what they actually are. It helps programmers
understand what they do and it makes it easier to keep track of them
-) use sub programs to make it easier for other programmers to see how different parts of a program work,
which can help the overall program faster. Sub program code can also be reused.
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SYNTAX ERRORS - where the program code syntax is not correct e.g. misspelt words, missing space, colon
etc. program does not run
U)GIC ERRORS - incorrect code that causes the program to run, but wrong output is produced
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