Chapter 56 - Subroutines and recursion

Question 1

What is a subroutine?

Answer 1

» A name block of code which performs a specific task within a program

Question 2

What are the 2 types of subroutines?

Answer 2

» Functions
» Procedures

Question 3

What is the difference between a function and a procedure?

Answer 3

» The function returns a value but the procedure doesn’t
» if there are values already in the subroutine, you use a procedure

Question 4

How can you call the subroutine from the main program and output it to the user?

Answer 4

» Simply write the subroutine name

Question 5

What does the first line of a subroutine specify?

Answer 5

» The interface for that subroutine

Question 6

What is modularity?

Answer 6

» Concept of breaking a large program or problem down into smaller chuncks

Question 7

What is the benefit of modularity?

Answer 7

» Each module carries out a single specific task

Question 8

What does a procedure do?

Answer 8

» Performs a set task and can take in a zero, 1 or 2 inputs

Question 9

What happens when a parameter is passed by a value?

Answer 9

» The value created for the subroutine being called is a copy of the original
» Held in a separate memory location once passed
» It is now a local variable

Question 10

What happens if you change the parameter inside the subroutine when you pass a value?

Answer 10

» It will not affect its value outside the subroutine

Question 11

What does it mean if a parameter is passed by a reference?

Answer 11

» The address of the parameter is passed to the subroutine
» A pointer that contains the memory address of the original variable is created

Question 12

What happens if you change the value in the parameter when passing by a reference?

Answer 12

» A change to this value within the called subroutine will also affect the value outside the subroutine
» It becomes a global variable

Question 13

What does it mean if you say a scope of a variable?

Answer 13

» Refers to where a variable is visible or accessible from inside the main program

Question 14

What is a global variable?

Answer 14

» A variable which is defined in the main program, outside any functions
» Has a global scope

Question 15

What are some disadvantages of using a global variable?

Answer 15

» Needs to be preserved in memory all the time, this means memory space is kept throughout the running of the program
» Makes it less memory efficient

Question 16

Why do we avoid using global variables?

Answer 16

» Increases complexity of the program - as they can be used by many difference parts of the program
» Make them harder to keep track of its value

» If you want to re-use code, you have to track and remember the value of the global variable

Question 17

Why do we used global variables?

Answer 17

» To use a variable which can be accessed from any parts of a program
» When a value needs to stay the same throughout the program

Question 18

What is a local variable?

Answer 18

» A variable which is defined in the procedure or function, and can be used only inside that function

Question 19

What are the advantages of using a local variable?

Answer 19

» Local variables in difference subroutines can have the same identifier
» Changing the value of a local variable in a subroutine, will not affect its value outside the subroutine

Question 20

What are the disadvantages of using a local variable?

Answer 20

» Can overwrite global variables with the same name
» Only exists during the execution of the program

Question 21

What the principle of encapsulation?

Answer 21

» The subroutine written according to this principle can be tested independently, and used in many different programs without the programmer needing to know what variable it uses

Question 22

What are the benefits of programming with subroutines?

Answer 22

» Relatively easy to understand and debug
» Can be tested independently
» It can be re-used
» Can use a modular approach

Question 23

When is a subroutine recursive?

Answer 23

» If its defined in terms of tiself

Question 24

What is recursion?

Answer 24

» When a subroutine calls itself from within its own subroutine

Question 25

What is sequence?

Answer 25

» Executing the instructions one after the other

Question 26

What is selection?

Answer 26

» A programming construct that allows a program to change direction depending on the outcome of a condition

Question 27

What is iteration?

Answer 27

» Programming construct which enables us to repeat sections of code

Question 28

What are 2 types of loops?

Answer 28

» Count controlled loops
» Condition controlled loop

Question 29

What are the 3 characteristics a recursive subroutine should have?

Answer 29

» Contain a stopping condition
» For any input value other than the stopping condition, the subroutine should call itself
» Stopping condition should be reachable within a finite number of times

Question 30

What are the problems if you don’t have the right characteristics of a recursive subroutine?

Answer 30

» May result in a stack overflow

Question 31

What is a programming paradigm?

Answer 31

» A style of coding

Question 32

How can we identify a global variable?

Answer 32

» Defined at the start of a program
» Exits throughout the prgoram
» Allows data to be shared throughout modules

Question 33

Why use local variables?

Answer 33

» Prevents variables being accidentally being overwritten

Question 34

Which variable is more memory efficient?

Answer 34

» Local

Question 35

Which variable is used when a value doesn’t tend to change throughout the run time of a program?

Answer 35

» Global

Question 36

Which variable is accessible throughout a program?

Answer 36

» Global

Question 37

Which variable increases complexity?

Answer 37

» Global

Question 38

Which variable allows data to be lost once a subroutine is no longer being used?

Answer 38

» Local

Question 39

Which variable is retained in memory permanently?

Answer 39

» Global

Question 40

What is the Recursive call?

Answer 40

» An instance of a subroutine calling itself

Question 41

What is a base case?

Answer 41

» A condition in a recursive ubroutine that when true, returns control to the subroutine that called it rather than running antoher recursive instance

Question 42

What are some advantages of recursion?

Answer 42

» Some problems are easier to think of recursively
» Recursive solutions can be more elegant

Question 43

What are some advantages of recursion?

Answer 43

» Some problems are easier to think of recursively
» Recursive solutions can be more elegant

Question 44

What are some disadvantages of recursion to iteration?

Answer 44

» It requires more memory in order to maintain the stack of calls
» If the space on the stack runs out, the program will run out
» Overheads of maintaing a stack means it will perform more slowly then iterative equivalent

Question 45

What are all parameter’s passed by in python?

Answer 45

» By value

Question 46

What is the difference between parameters and arguements?

Answer 46

» Parmaters are the variables whose values are taken in by a subroutine and the arguements are the values passed to them

Question 47

Describe the use of local variables

Answer 47

» Local scope - only affect the variable inside the subroutine - reduces complexity of code when co sharing
» Store identifer with the same name
» Less memory used then global

Question 48

State two features of global variables that distinguish them from local variables

Answer 48

» Can be accessed at any point in a program and are defined at the start of the program
» Continously held in memory, and the variable data does not get lose when the subroutine ends