Unit 11 - Programming Techniques

Question 1

define iteration

Answer 1

a sequence of instructions is repeated multiple times

Question 2

examples of iteration

Answer 2

• for loop
• do…until
• while

Question 3

difference between do…until and while loops

Answer 3

• while loop condition is tested at the start
• do..until condition is tested at the end. therefore code is always run at least once

Question 4

define selection

Answer 4

changing the flow of the program

Question 5

selection commands in LMC

Answer 5

BRA
BRZ
BRP

Question 6

define IDE

Answer 6

Integrated Development Environment - software which enables you to enter, edit, compile (or interpret) and run your programs. many IDEs have debugging facilities to help you find the logic errors in a program

Question 7

features of IDEs for code writing

Answer 7

• line numbers
• automatically indent code
• auto-complete commands
• comment or un-comment a region

Question 8

features of IDEs for debugging

Answer 8

• set a breakpoint in the program which will cause the program to stop on that line
• set a watch on a variable so that its value is displayed each time it changes
• step through a program one line at a time
• trace the execution of the program

Question 9

define identifier

Answer 9

name that points to the memory location

Question 10

define assignment

Answer 10

assigning a value to a memory location

Question 11

define variable

Answer 11

a named location in memory where data can be stored and that can be changed throughout the program

Question 12

define constant

Answer 12

cannot be the target of an assignment as you have to change the source code and then recompile. reduce the risk of errors by reducing access to the memory location

Question 13

define subroutine

Answer 13

a set of instructions with a name that when called changes the sequence of a program

Question 14

difference between procedures and functions

Answer 14

• a function returns a value
• call statement differs

Question 15

define parameters

Answer 15

appear in subroutine definitions and remain the same

Question 16

define arguments

Answer 16

may change because they appear in subroutine calls

Question 17

passing by reference(value)

Answer 17

the address of the argument calling the statement is passed to the corresponding parameter in the subroutine. any calculation performed on that parameter in the subroutine will change the value of the corresponding argument in the calling routine

Question 18

define global variables

Answer 18

defined in the main program and can be re-used in subroutines

Question 19

advantages of local variables

Answer 19

• subroutine will be independent of a particular program and can be re-used in different programs
• there is no chance of accidentally changing a variable in the main program that is used in a subroutine or vice versa
• subroutine is self-contained
• uses less memory

Question 20

define modular programming

Answer 20

• means breaking down a major task into smaller subtasks
• these subtasks may be further broken down until each ‘module’ performs a single function

Question 21

advantages of modular programming

Answer 21

programs are more quickly and easily written:
- large programs are broken down into subtasks that are easier to program and manage
- each module is individually tested
- modules can be re-used several times in a program
- large programs are much easier to debug and maintain

Question 22

characteristics of recursion routines

Answer 22

• a stopping condition or base case must be included which when met means that the routine will not call itself and start to ‘unwind’
• for input values other than the stopping condition, the routine must call itself
• the stopping condition must be reached after a finite number of calls

Question 23

use of call stack

Answer 23

• every time a subroutine is called, the return address is put on the call stack
• even with a stopping condition, the recursive routine can only be called a limited number of times or the stack will overflow with the maximum memory capacity