8.2 introduction to software development

how do you understand a problem (understanding the problem)

how do you understand a problem (understanding the problem)

1. identify requirements and parameters of the problem

2. determine the steps that will solve the problem

3. check and test the solution

what is an IPO diagram (understanding the problem)

used to describe data elements that enter a system/subsystem, processors that will occur, and the data elements that will then leave the system

what is the top down approach (abstraction/refinement)

breaking down large complicated problems into smaller problems that are easier to solve

what is a program made of (abstraction/refinement)

modules and subprograms

what are modules (abstraction/refinement)

written separately and brought together to form a whole

what is algorithm/main program known as

the driver module

what are subprograms (abstraction/refinement)

used within the main program section, used often in top-down method

what are data flow diagrams and when are they used (abstraction/refinement)

describes the path of data in system, initial DFD represents one whole system as a single process (known as a CONTEXT DIAGRAM/LEVEL 0 DFD)

1. used during design processes

what are structure charts (abstraction/refinement)

represents a system by showing the separate modules/subroutines

what do the shapes in structure charts mean (abstraction/refinement)

1. rectangle

2. empty circle arrow

3. filled circle arrow

4. diamond

5. curved arrow

1. module

2. flow of data

3. flag to show processing being doing

4. decision

5. loop

what are system flowcharts (abstraction/refinement)

representing a system to show the flow of data

what do the shapes of system flowcharts mean (abstraction/refinement)

1. parallelogram

2. rectangle with a chomp

3. pencil looking shape

4. slanted roof

5. rectangle with a fold on the top left

6. rectangle

7. rhombus

8. tape

9. cylinder

10. diamond

11. line

1. input/output

2. paper document

3. online display

4. online input

5. punched card

6. process

7. manual operation

8. magnetic tape

9. disk drive

10. decision

11. telecommunication link

what is the difference between a system flowchart and a program flowchart

system flowcharts do not use a start/end system and dont represent complex logic

program flowcharts are used to represent the logic in an algorithm

what are the different data types (data types)

integer, string, floating point, boolean, date, array, record, file

what is an integer (data types)

whole numerical data stored as 2 bytes

what is a string (data types)

a sequence of characters

what is a floating point (data types)

numbers with decimal places and requires more data than an integer

what is a boolean (data types)

simplest data type with only two possible values, true or false

what is a data structure (data types)

literally top-down

what is a one-dimensional array (data types)

allows a variable to store a number of related data items, that are the same type, rather than just one item

what is a record (data types)

used to link data items that are related but are DIFFERENT types

how are records use in sequential files (data types)

records being stored in a way that only allows access to a record if all previous records have been processed

usually end-of-file (EOF) marker used at the end of a file

what is a data dictionary (data types)

information of variables including name, data type, size, description and examples

what are structured algorithms

a series of steps or instructions designed to solve a problem

what is a control structure (structured algorithms)

literally a flowchart

what is a sequence (structured algorithms)

a simple sequence of instructions

what is a selection and examples (structured algorithms)

a selection between two or more different courses of actions

eg. binary selection (if, then, else) and multiway selection (casewhere)

what is repetition and examples (structured algorithms)

the repetition of a set of instructions a number of times

eg. pre-test (while, endwhile) and post-test (repeat, until) loops

what is pseudocode (structured algorithms)

relies on indented words and use of keywords (in caps) to highlight structure of an algorithm

BEGIN

END

what are program flowcharts (structured algorithms)

a pictoral or graphical method of describing an algorithm

what do the shapes of flowcharts mean

1. rounded rectangle

2. rectangle

3. diamond

4. parallelogram

5. weird chomped rectangle

6. rectangle with lines

7. arrow

1. start and end of a flowchart

2. process

3. decision

4. input/output

5. paper document

6. subroutine

7. flow of logic

how do you load an array and print its contents (structured algorithms)

BEGIN

→ OPEN …………. FOR INPUT/OUTPUT

→ READ …… FROM …………..

→ → WHILE NOT EOF

CLOSE …………..

END

what and how do you use stubs (structured algorithms)

temporary section of code used to reduce the places that you need to look to find an error, used to represent incomplete modules

what are structured algorithms good for (structured algorithms)

to improve the clarity, quality, and development time of a computer program

what are meta-languages (implementing software solutions)

describing the syntax of a programming language

• made by john backus in mid to late 1950s

what do EBNF diagrams look like (implementing software solutions)

1. {}

2. []

3. ()

4. |

5. =

6. <>

1. repetition, DOESNT have to be carried out

2. optional

3. grouped elements

4. or

5. is defined as

6. needs to be defined

what do railroad diagrams look like (implementing software solutions)

1. lines

2. rectangles

3. circles/rounded rectangles

1. lines: branches (can be loops/optionals)

2. rectangles: pre-defined element

circles/rounded rectangles: fixed element

what are syntax errors (implementing software solutions)

1. occurs how

2. when is it discovered

3. ways to avoid

1. occurs when programmers fails to follow grammar rules

2. during translation process it will stop and an error message will appear

3. take care when typing code and desk check

what are runtime errors (implementing software solutions)

1. occurs how

2. when is it discovered

3. ways to avoid

1. trying to divide by 0, reading data from a non-existent file, finding the square root with negative numbers, outside of a boundary

2. whilst a program is running it will randomly quit

3. be aware of where these types of errors may occur

what are logic errors (implementing software solutions)

1. occurs how

2. when is it discovered

3. ways to avoid

1. condition does not check boundary values, reusing variable names which still contain old values

2. when operations are performed invalid

3. desk check the algorithm

what are flags used for (implementing software solutions)

used to check if a section of code has been processed, boolean, set to false and set to true if code is executed

what are some reasons for maintaining code (maintaining software solutions)

1. changing user requirements

2. upgrading the user interface

3. changes in the data to be processed

4. introduction of new hardware or software

5. changing organisational focus

6. changes in government requirements

7. poorly implemented code

how do you create solutions that are easy to maintain (maintaining software solutions)

1. use of variables instead of literal constants

2. use of meaningful variable names

3. explanatory comments in the code

4. use of standard control structures with appropriate indentation

5. appropriate use of white space to improve legibility of the source code

6. a clear and uncluttered mainline

7. one logical task per subroutine

8. meaningful names for subroutines and modules