CS UNIT 9

• Algorithm design and problem-solving involve computational thinking skills to create software solutions that work with associated computer hardware.
• Computational thinking involves abstraction and decomposition.
• Skills are developed through practice, including coding and testing.
• Programming languages used include Java, Python, and VB.NET.

What you should already know

• Procedure: a series of actions conducted in a certain order.
• Function: a relation from a set of inputs to a set of permissible outputs with the property that each input is related to exactly one output.
• Algorithm: a process or set of rules to be followed in calculations or other problem-solving operations, especially by a computer.
• Structured English: a method of showing the logical steps in an algorithm, using straightforward English words for commands and mathematical operations.
• Flowchart: a diagram representing an algorithm.
• Pseudocode: a method of showing the detailed logical steps in an algorithm, using keywords, identifiers with meaningful names, and mathematical operators.

Computational Thinking Skills

• Computational thinking uses several techniques, including abstraction, decomposition, algorithms, and pattern recognition.

Using Abstraction

• Abstraction is extracting essential information and ignoring irrelevant details to develop clear models for complex problems.
• It creates simplified models suited for specific purposes by removing unnecessary characteristics.
• Abstraction is used in maps, calendars, and timetables.
• Benefits include reduced program development time, smaller program size, and greater customer satisfaction by meeting requirements without extraneous features.
• The steps include identifying the purpose of the model, identifying sources of information and using gathered information.
• Maps are frequently used and take different forms depending on the identified use.

Using Decomposition

• Decomposition is breaking a complex problem into smaller parts to examine and understand them easily
• Smaller parts can then be further subdivided again.
• Decomposition helps simplify complex problems by breaking them down into manageable parts.
• Pattern recognition identifies similar parts that could use the same solution, this leads to reusable program code in the form of subroutines, procedures, and functions.
• Each final part is defined as a separate program module that can be written and tested separately.
• Program modules already written and tested can also be identified and reused.

Algorithms

• An algorithm is an ordered set of steps to be followed in the completion of a task.

Writing algorithms that provide solutions to problems

• Structured English uses straightforward English words for commands and mathematical operations.
• A flowchart shows the steps required for a task and the order in which they are to be performed using symbols linked with flow lines.
• Pseudocode uses keywords, identifiers with meaningful names, and mathematical operators to represent a solution.
• Structured English steps are usually numbered.
• Structured English and Pseudocode are useful for representing programming solutions to problems.

Writing simple algorithms using pseudocode

• Each line of pseudocode is a single step in an algorithm.
• Keywords used in pseudocode are set out using a fixed width font and indentation of four spaces, except for THEN, ELSE, and CASE clauses that are indented by two spaces.
• Identifier names should be meaningful containing A-Z, a-z, and 0-9, and should start with a letter.
• Identifiers are usually case insensitive.
• It is good practice to keep track of identifiers in an identifier table.

Pseudocode statements

• To input a value: INPUT StudentName
• To output a message or a value or a combination: OUTPUT "You have made an error" , OUTPUT StudentName, OUTPUT "Student name is ", StudentName
• To assign a value to a variable (the value can be the result of a process or a calculation): Counter ← 1, Counter ← Counter + 1, MyChar ← "A", LetterValue ← ASC(MyChar), StudentMark ← 40, Percentage ← (StudentMark / 80) * 100, Oldstring ← "Your mark is", NewString ← OldString & " ninety-seven"
• Operators used in pseudocode assignment statements: +, -, *, /, &, ←
• To perform a selection using IF and CASE statements are used.

Iteration

• To perform iteration, FOR, REPEAT-UNTIL and WHILE loops are used.
• FOR loop: FOR Counter ← 1 TO 10, FOR Counter ← 1 TO 10 STEP 2
• A FOR loop has a fixed number of repeats, the STEP increment is an optional expression which must be a whole number.
• REPEAT loop: REPEAT ... UNTIL Number > 0
• Statements in a REPEAT loop are always executed at least once.
• WHILE loop: WHILE Number >= 0 DO...ENDWHILE
• Statements in a WHILE loop may sometimes not be executed.
• WHILE and REPEAT loops make use of comparisons that result in true or false.

Writing pseudocode from a structured English description

• Wordings in structured English just needs to be unambiguous and easily understandable.
• Identifying variables required in tables including input, output, and results of calculations is important.
• Each structured English statement can be used to write one or more pseudocode statements, while keeping the same order.

Writing pseudocode from a flowchart

• Flowcharts are diagrams showing the structure of an algorithm using an agreed set of symbols.
• Flowcharts can be used to identify any variables required to complete an identifier table.
• Each flowchart symbol can be used to identify and write one or more pseudocode statements.

Stepwise refinement

• Stepwise refinement involves breaking a problem down into smaller, manageable parts, with each step written as a statement in a high-level programming language.