unit 2b - programing techniques

Question 1

what is a scope?

Answer 1

the area of a program where an item (variable, constant, subroutine etc.) is recognised by the program

Question 2

what is a subroutine?

Answer 2

a selection of code that you can group together under a name and then call later in the program

example:
SUBROUTINE showKeys()
OUTPUT “keyboard controls”
OUTPUT “=============”
ENDSUBROUTINE

showKeys()

note that the subroutine above has no parameters hence the empty brackets

Question 3

what is data validation?

Answer 3

it ensures that the data entered is the right type

Question 4

what can validation not ensure?

Answer 4

it cannot ensure that the user has not typed in the wrong value or if there is a spelling mistake but rather if the data is reasonable and conforms to a set of rules

Question 5

what are the 5 types of validation checks?

Answer 5

range check, type check, length check, presence check, format check

Question 6

what does a range check do?

Answer 6

checks whether a number or date is within a sensible/allowed range

Question 7

what does a type check do?

Answer 7

checks if the data is the right type eg. string or integer

Question 8

what does a length check do?

Answer 8

checks if the data entered is of the right lengtheg. between a certain number of characters

Question 9

what does a presence check do?

Answer 9

checks if data has been entered into a field or not ie. in case the field has been left blank

Question 10

what does a format do?

Answer 10

checks if the data is the correct format eg. if was a postcode or email address

Question 11

what is verification?

Answer 11

it is used to double check that the data has been typed in correctly

Question 12

what is double-entry verification?

Answer 12

example: if a user is making a new password, they may be asked to enter it twice and if the two passwords don’t match, they’ll be asked to enter it again

Question 13

what is authentication used for?

Answer 13

used to make sure a person is who they claim to be - checks this by identifying a valid username and password

Question 14

how can programs be made easier to understand and maintain?

Answer 14

• comments to show who wrote the program and when
• comments to explain what the harder parts of code do
• comments to explain the functionality of each subroutine (function or procedure)
• meaningful variable names
• a modular structure

Question 15

what are trace tables used for?

Answer 15

used to determine the outputs from a program as it runs. enables a programmer to find errors in their programs

Question 16

how do your create a trace table?

Answer 16

• make a column of each variable used in the order in which they appear
• record the value of each variable as it changes

Question 17

why is a trace table useful?

Answer 17

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

Question 18

what are logical errors?

Answer 18

any error that isn’t a syntax error so the program will run/compile but not as intended by the programmer

Question 19

what are syntax errors?

Answer 19

where the code written doesn’t conform to the rules of the language - the program can’t be run (and will return an error) if there are syntax errors

Question 20

what is testing and why is it important?

Answer 20

it is important that the programs are fully to find logical errors
a test plan tests for normal data, boundary data and erroneous data

Question 21

what is normal data?
program: number between 1 and 100

Answer 21

normal data would be 5 (checks a single-digit) and 14 (checks two digits)

Question 22

what is boundary data?
program: number between 1 and 100

Answer 22

so boundary data would be the values either side of the boundary.
- 1 (checks the lowest valid data)
- 100 (checks highest valid data)
- 0 (checks invalid data at the boundary)
- 101 (checks invalid data at the boundary)

Question 23

what is erroneous data?
program: number between 1 and 100

Answer 23

erroneous data would something completely out of the range like -5 (checks a negative number) or 1012 (checks a large number) or “#$%” (checks that the data is of the wrong type) is rejected

Question 24

what are two techniques to finding logic errors?

Answer 24

• trace table - traces through a program to scan for errors
• inserting output statements at various points in the program to find the values of variables

Question 25

what are two types of subroutines?

Answer 25

functions and procedures

Question 26

what can be passed to both procedures and functions and which of the two return a value?

Answer 26

values can be passed to both procedures and functions and functions will return a value after processing has taken place

Question 27

what are built in subroutines and what are some examples in python?

Answer 27

they are built in procedures and functions to perform common tasks

examples:
- print(“hello”) - procedure
- input (“type in your name:”) - function
- random(1,6) - function

Question 28

what is one difference between procedures and functions?

Answer 28

• procedures execute code in a subroutine - but they don’t return anything
• functions will return something, so input returns what the user typed, random returns a number

Question 29

what is a function?

Answer 29

• basically a procedure that returns a value at the end

example:
SUBROUTINE sum (a,b)
total <- a + b
return total
ENDSUBROUTINE

answer <- sum(5,3)
OUTPUT answer

Question 30

what are parameters?

Answer 30

a variable names in a subroutine heading that will receive and whatever value you pass through it

in sum(a,b), a and b are parameters

Question 31

how do you call a subroutine?

Answer 31

write the subroutine name and add parameters

example:
SUBROUTINE averageScore (totalScore, numScores)
avg <- totalScore / numScores
return avg
ENDSUBROUTINE

to call the function
OUTPUT “entire the total:”
total <- USERINPUT
OUTPUT “enter the number of scores:”
n <- USERINPUT
OUTPUT averageScore(total,n) «< calling
the function

Question 32

why are subroutines useful?

Answer 32

• useful to break up a large program into self contained units
• each subroutine can be tested separately to make sure it works correctly
• many programmers can work on a lrage program at the same time, cutting down development time
• subroutines can be re-used in other programs because they can be stored in a subroutine library
• program maintenance is much easier because subroutines can be easily modified

Question 33

what are local variables?

Answer 33

they only exist while the subroutine is executing and are only accessible within the subroutine

Question 34

what are global variables?

Answer 34

they are accessible anywhere in the program

Question 35

how are global variables written in pseudocode?

Answer 35

using the keyword global score

Question 36

what are global and local constants?

Answer 36

they follow the same rules as global and local variables except a constant cannot be changed once declared

Question 37

what is an advantage of using local variables?

Answer 37

local variables keep a subroutine self-contained so it can be used in any program without variable names conflicting with those used in the main program

Question 38

how should subroutines be written?

Answer 38

• they should be able to take any inputs (through parameters) and if necessary return values
• they should be written in a modular way so that they can be reused multiple times in the program or in other programs

Question 39

what is the structured approach?

Answer 39

subroutines should be well-documented to show:
- the parameters that the subroutine takes, what they are used for and what data types are needed
- the purpose of the subroutine
- the return value and its data type

Question 40

what are advantages to using the structured programming technique?

Answer 40

• the modularised approach of using subroutines helps to decompose large problems
• programmers only need to use the interfaces of subroutines - the parameters and return values so they don’t need to worry about the workings of each subroutines
• programs will have fewer bugs and be easier to maintain