Programming techniques

Question 1

what are some common programming constructs used in structured programming?

Answer 1

• sequence
• iteration
• branching

Question 2

define “sequence”

Answer 2

code is executed line by line, from top to bottom

Question 3

what is selection?

Answer 3

when a question is asked which has a Boolean answer, and depending on the answer the program takes 1 of 2 courses of action, after which the program moves onto the next event
ie. an if… then… else… statement

Question 4

when are nested if statements used and what do they look like?

Answer 4

used when it isn’t enough to ask one question:

if….
….
if…..
…..

Question 5

what are case statements?

Answer 5

use these to ask lots of questions (in Python this is an elif statement)

Example:

case k of:
1: print(“gold”)
2: print(“silver”)
3: print(“bronze”)

Question 6

what is iteration?

Answer 6

a process wherein a set of instructions or structures are repeated in a sequence a specified number of times or until a condition is met

Question 7

what are the 2 major groups of loops?

Answer 7

• count-controlled
• condition-controlled

Question 8

what is a count controlled loop?

Answer 8

a loop which repeats the instructions within it until the counter reaches a certain value
eg. a for… next loop

Question 9

what is a condition controlled loop?

Answer 9

a loop which repeats the instructions within until a condition is met (this may still be a value)
eg. a while… loop

Question 10

what is a post test iteration? give an example

Answer 10

tests the condition at the end of the sequence so will always be run once

example:

repeat
print “hello world”
x = x+1
until x = 10

Question 11

what is a pre test iteration?

Answer 11

condition is checked before entry into the iteration so if the condition isn’t met, it won’t run

Example:

while x < 10:
print “hello world”
x = x+1
endwhile

Question 12

what is branching?

Answer 12

when control is passed to a different sequence of instructions, rather than completing the next line
eg. in assembly: BRA, BRZ, BRP
used for functional + procedural calls

Question 13

how does branching work?

Answer 13

uses a stack to keep track of each branch call, so that it can retrace its steps back to the main program

Question 14

what is a function?

Answer 14

a subprogram that can be called from elsewhere in the program - interrupting the natural sequence of the program
returns a value to the main program
can have parameters

Question 15

what is a procedure?

Answer 15

almost the same as a function but doesn’t return a value on completion

Question 16

what is a library?

Answer 16

a collection of functions

Question 17

what are the basic rules that apply to loop structures?

Answer 17

• must have a terminating condition
• must have a sequence of code that achieves a task
• can only be nested within themselves
• cannot overlap - must be wholly contained within another

Question 18

what are some advantages of using the case structure over nested if statements?

Answer 18

• easier to read - structured nature makes clear which statement is being checked and what actions taken based on conditions
• more efficient
• code is more organised + easier to maintain
• handles complex logic better than nested if, especially if there are many cases to consider

Question 19

what are some advantages of using nested if statements over the case structure?

Answer 19

• more versatile

Question 20

what is a recursive function?

Answer 20

• a function that calls itself
• continues to call itself until stopping condition is reached
• hypothetically easier to program - less code = less to debug
• every recursive can be written as iterative

Question 21

how does recursion work?

Answer 21

• each time the function calls itself a new stack frame is created within call stack - stores parameters, local variables + return addresses
• finite no of stack frames are created until base case/stopping condition is reached
• recursions are then resolved and stacks created are removed

Question 22

what is a stack overflow error?

Answer 22

call stack running out of memory to contain stack frames created during recursion

Question 23

what are the advantages of recursion?

Answer 23

• functions using it can be represented using fewer lines of code - less prone to errors
• but only good if base case is clearly defined so stopping condition is reached after finite number of function calls

Question 24

what are the disadvantages of recursion?

Answer 24

• inefficient use of memory - creating stack is memory intensive
• stack overflow would cause the program to crash
• difficult to trace esp with more function calls
  (also i just really hate it i dont get it)

Question 25

what is a scope?

Answer 25

the section of code in which a variable is available

Question 26

what is a local variable?

Answer 26

a variable declared inside a subroutine + can only be accessed by the subroutine + data contained in it is destroyed at the end of the subroutine takes precedence over a global variable with the same name

Question 27

why are local variables good?

Answer 27

- variables with the same name can be used in different subroutines and be unaffected by each other - subroutines are kept self-contained - variables can't be affected by code outside the subroutine

Question 28

what is a global variable?

Answer 28

a variable that is defined at the start of a program + exists throughout including in functions + procedures - allows data to be shared between modules overriden by local variables with the same name

Question 29

why is using global variables not recommended?

Answer 29

- can be unintentionally overwritten/edited - requires more memory than local variables - it is only deleted when the program terminates, not as soon as the subroutine is completed

Question 30

what are the 2 methods of parameter passing?

Answer 30

- passing by value - passing by reference

Question 31

what is parameter passing by value?

Answer 31

the variable being used to transfer the value to the procedure does not get altered itself, only a copy of its value is passed + discarded at the end of the subroutine - kind of treated like a local variable

Question 32

what is parameter passing by reference?

Answer 32

the variable being used to pass the parameter gets referenced and therefore irrevocably altered by the procedure address of parameter is given to subroutine -> value of parameter is updated here

Question 33

are functions passed by value or reference in an exam by default? what is the notation if its something different?

Answer 33

- by default it will be passed by value unless specified - the format is: function multiply(x:byVal, y:byRef)

Question 34

what is modularity?

Answer 34

the process of breaking down a problem into component tasks, so that each module carries out a specific task

Question 35

what are the advantages of modularity?

Answer 35

- breaks the problem down into manageable chunks - can divide tasks amongst a team - tasks can be achieved concurrently - maintenance is much easier - modules can be reused easier (libraries, functions, procedures) - modules are pretested

Question 36

what is an IDE and what is it used for?

Answer 36

it is an Integrated Development Environment - provides a set of tools to make it easier for programmers to write, develop + debug code

Question 37

what are some tools available in an IDE to identify logic errors?

Answer 37

- setting breakpoints - setting a watch on a variable - step through the program

Question 38

what is the breakpoint feature of an IDE?

Answer 38

- This allows the user to set a point in the program at which it will stop - can be a line or a condition - you can see whether the program executes correctly up to that line - helps pinpoint the error

Question 39

what is the variable watch feature of an IDE?

Answer 39

displays the value of a variable each time it changes so can observe how it changes in real time through the execution of the program - useful to pinpoint errors

Question 40

what is stepping through the program using an IDE?

Answer 40

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

Question 41

what is the source code editor?

Answer 41

aims to make the coding process easier by providing features such as autocompletion of words, indentation, syntax highlighting and automatic bracket completion

Question 42

what is another debugging tool provided by the IDE?

Answer 42

run-time detection of errors - provides a guide to where in the code the error might be through line numbers and highlighting

Question 43

what is the purpose of testing?

Answer 43

to try and uncover undetected errors

Question 44

how should a program work if its been done perfectly?

Answer 44

- should work correctly whatever data is inputted - valid data = everything is smooth - invalid data = detect + report this + ask user to enter valid data - some valid data might cause the program to crash if you haven't allowed certain values

Question 45

what are the 3 types of test data?

Answer 45

- normal data - data within the range that you would expect + of the data type you would expect - boundary data - data at the ends of the expected range - test these to make sure these give the expected results - erroneous data - data that is either just outside the expected data range or is of the wrong data type

Question 46

what is a class in object-oriented programming?

Answer 46

a template for an object which defines the state + behaviour of an object

Question 47

what is the state of an object in OOP?

Answer 47

it is given by attributes which give an objects properties

Question 48

how are behaviours of an object defined in OOP?

Answer 48

they are defined by the methods associated with the class which describes the actions it can perform

Question 49

what is instantiation?

Answer 49

the process by which classes can be used to create objects

Question 50

what is an object?

Answer 50

a particular instance of a class - there can be multiple instances of a class with the same set of attributes + methods

Question 51

what is encapsulation?

Answer 51

attributes are declared as private so can only be altered by public methods used to implement the principle of information hiding

Question 52

what is the principle of information hiding?

Answer 52

when programs are made less complex by protecting data from being accidentally edited by other parts of the program