2.2.1 Programming Techniques

Question 1

Programming constructs

Answer 1

• a programming construct determine the order in which lines of code are executed
• 3 main programming constructs
• selection
• iteration
• sequencing

Question 2

Sequence

Answer 2

• code is executed line by line in sequence from top to bottom

Question 3

Iteration

Answer 3

• repeating a line or block of code using a loop
• can either be count controlled or condition controlled

Question 4

Count controlled

Answer 4

• (for loop)
• is used when the number of iterations is known before execution and the block of code is executed a certain number of times

Question 5

Condition controlled

Answer 5

• used when the number of iterations is not known so the block of code is only executed while a condition is met
• while loop, do until loop

Question 6

Branching

Answer 6

• the particular block of code is run if a specific condition is met
• eg. If else statements

Question 7

Recursion

Answer 7

• is when a subroutine/function calls itself from within its own subroutine/function [1]
• the function continues to call itself until a base case/stopping condition is met [1]

Question 8

Importance of base case

Answer 8

• without a base case, a recursive function may call itself indefinitely resulting in a stack overflow
• the base case should be reachable within a finite number of times
• for input values other than the stopping condition, the function must call itself

Question 9

Recursion benefits

Answer 9

• quicker to write/ requires less lines of code [1] as some functions are naturally recursive
• can reduce the size of a problem with each call [1]
• recursion is suited to certain problems e.g problems involving trees or factorials [1]

Question 10

Recursion drawbacks

Answer 10

• more difficult to trace as each frame on the stack has its own set of variables [1]
• requires more memory compared to the equivalent iterative algorithm in order to maintain the stack of calls [1]
• risk of stack overflow if memory runs out e.g due to too many calls [1]

Question 11

Scope

Answer 11

• the section of code in which a variable can be accessed
• a local variable within a subroutine takes precedence over a global variable with the same name

Question 12

Local variables

Answer 12

• can only be accessed with the subroutine in which they were defined [1]
• multiple local variables with the same name can exist in different subroutines [1]/ same variable name be used in other modules without causing errors/overwriting
• are deleted once the subroutine ends [1]
• can overwrite global variables with the same name [1]

Question 13

Global variables

Answer 13

• can be accessed across the whole program [1] (so no need to pass as a parameter or redeclare
• is used when a value needs to be accessible from various parts of a program [1]
• value remains the same irrespective of where it is accessed [1]
• e.g values of constants like pi or VAT rate [1]
• not deleted until the program terminates so requires more memory

Question 14

Global variables drawbacks

Answer 14

• make it difficult to integrate modules [1]
• increase the complexity of a program [1]
• they may cause conflicts with names in other modules [1]
• may be modified unintentionally when the program is complex [1]

Question 15

Modular programming

Answer 15

• programs are split into separate self contained modules [1]
• which can be written/tested individually [1]
• modules can be subdivided further into smaller modules [1]

Question 16

Modular programming advantages

Answer 16

• modules can be reused in the current project and future projects which saves time [1]
• modules can be shared between programmers so work is easier to divide between a team [1]
• this reduces development time as work takes place in parallel [1]
• modules can be allocated according to the programmers/team members expertise [1]
• modules are easier to maintain/test/debug as each subroutine can be tested independently before integration [1]

Question 17

Function

Answer 17

• a named block of code that performs a specific task and must always return a single value [1]

Question 18

Procedure

Answer 18

• a named block of code that performs a specific task but does not have to return a value [1]

Question 19

Parameter

Answer 19

• an item of data that is passed into a subroutine and can be discarded at the end of the subroutine [1]

Question 20

Parameter passing

Answer 20

• by value
• by reference

Question 21

Passing by Value

Answer 21

• a local copy of the value/data is passed into the subroutine and discarded at the end of the subroutine [1]
• so only the copy is changed [1]
• this means value of the original data is unchanged/remains unaffected [1]

Question 22

Passing by Reference

Answer 22

• the address/memory location of the data is sent [1]
• so changes are made to the original data/changes the value in the variable passed [1]
• changes remain even after the subroutine exits [1]

Question 23

IDE ( integrated development environment)

Answer 23

a program used for developing programs which provides a set of tools to make it easier for programmers to write, develop and debug code [1]

Question 24

IDE features

Answer 24

• Stepping
• break points
• error diagnostics
• variable watch window
• syntax highlighting
• autocomplete

Question 25

Stepping

Answer 25

- runs the program line by line to check variable values at each stage - this allows programmers to watch the effects of each line of code [1]

Question 26

Breakpoints

Answer 26

Stop the program running at a set point to check the value of variables [1]

Question 27

Error diagnostics

Answer 27

To locate and fix errors

Question 28

Variable watch window

Answer 28

- to watch how variables change as the program executes [1]

Question 29

Syntax highlighting

Answer 29

- to identify keywords,variables and help identify syntax errors [1]

Question 30

Autocomplete

Answer 30

- start typing a command/identifier and it completes it, this avoids spelling mistakes and saves time [1]