Algorithms (Cambridge (CIE) A Level Computer Science): Flashcards

An oval for start and end, a parallelogram for input and output, and a rectangle for processes.

On a flowchart, arrows show the sequence of operations.

An identifier table is used when writing pseudocode to keep track of all the identifier names used in an algorithm.

An identifier is the name given to a variable, constant, array, procedure or any other named element in the pseudocode.

It helps you stay organised when designing an algorithm, ensures consistent naming, and makes it easier to understand what each identifier stores or does.

An identifier must start with a letter, either A-Z or a-z.

Letters, digits (0-9) and underscores.

An identifier name may not contain symbols or accented characters.

False.

Identifiers are case sensitive, so Total and total are not treated as the same identifier.

An input is data or information being entered or taken into a program before it is processed in the algorithm.

From a user, using a keyboard, mouse, controller or microphone, and from sensors measuring temperature, pressure or movement.

The INPUT command, written as INPUT <identifier>.

A process is a doing action performed in the algorithm that transforms inputs into the desired output.

The central processing unit (CPU).

Comparing two numbers and calculating an average.

An output is the result of the processing in an algorithm, and usually the way a user can see whether the algorithm works as intended.

Numbers from a calculation, text, images, and actions such as triggering events.

Values are output from an algorithm using the OUTPUT command.

Separate the values with commas, for example OUTPUT "First name: ", Fname, "Surname: ", Sname.

The inputs are Length and Width, the process is Length * Width, and the output is the Area.

Sequence refers to lines of code which are run one line at a time, in the order they are written, from the first line to the last.

Any instructions that are out of sequence can lead to unexpected behaviour or errors.

Selection is when the flow of a program is changed depending on a set of conditions, and the outcome determines which block of code runs next.

IF ... THEN ... ELSE and CASE.

IF ... THEN ... ELSE is used for binary decisions that are true or false, whereas CASE is used for multiple specific options.

Validation, calculation, and making sense of a user's choices.

False.

← is used for assignment. = is used in a comparison, such as IF Number MOD 2 = 0 THEN.

Iteration means repeating a line or block of code using a loop, so a task can be performed multiple times until a condition is met.

Count-controlled, post-condition and pre-condition.

FOR ... TO ... NEXT, which repeats a fixed number of times.

A pre-condition loop, WHILE ... ENDWHILE, checks the condition before running the block. A post-condition loop, REPEAT ... UNTIL, runs the block at least once and checks the condition after.

A REPEAT ... UNTIL loop checks its condition after running the block.

False.

A WHILE loop checks the condition before running the block, so it may run zero times. It is REPEAT ... UNTIL that runs at least once.

Write it in Structured English, build an identifier table, then write the pseudocode.

In the discount example, a customer who has a discount code receives 10% off the price.

The original price of the item.

TRUE if the user has a discount code.

The price after the discount is applied.

DiscountAmount ← ItemPrice * 0.10

FinalPrice ← ItemPrice - DiscountAmount

ENDIF

True.

The line is IF HasDiscount = TRUE THEN, where = is used as a comparison, not as an assignment.

Build an identifier table, work out the flowchart structure by deciding which symbol each statement maps to, then draw the flowchart.

False.

The identifier table is the first step, written before the flowchart structure is worked out and before the flowchart is drawn.

The number entered by the user.

A parallelogram, which is the input/output symbol.

A diamond, which is the decision symbol, because it checks whether the number is divisible by 2.

It checks whether the number is divisible by 2, which means the number is even.

In the odd/even example, if Number MOD 2 = 0 is false, the algorithm outputs the message Odd.

An oval.

The arrows indicate the flow of control.

Stepwise refinement is the process of breaking down a complex problem into smaller, more manageable sub-problems in a logical order.

Each sub-problem is refined step by step until it is simple enough to be solved with a single subroutine or module.

Stepwise refinement breaks a complex problem into sub-problems in a logical order.

Decomposition is the general concept of breaking a problem into smaller parts, top-down design is the strategy used to perform decomposition, and stepwise refinement is the process used in top-down design to gradually refine each major task into simpler sub-tasks.

False.

Top-down design is the strategy. Stepwise refinement is how top-down design is implemented.

Stepwise refinement ensures the overall problem is solved in a structured and efficient way.

It helps developers understand and organise the structure of the program.

It makes testing and debugging easier through unit testing of individual subroutines.

It breaks tasks into reusable components.

Tasks can be divided between team members.

Each subroutine should be clear and focused on a single task, simple enough to implement directly, and should not need further breakdown.

False.

Each subroutine should be clear and focused on a single task.

To calculate grades for all students in all classes.

For each question, mark the question and store the mark, then sum the marks for all questions in the assessment.

Add together the grades from all assessments, divide by the number of assessments, then store the average.

It repeats Steps 1 and 2 for every student in the class, so the process covers each class in turn.