GCSE High and Low Level Languages (14-16 years)
- An editable PowerPoint lesson presentation
- Editable revision handouts
- A glossary which covers the key terminologies of the module
- Topic mindmaps for visualising the key concepts
- Printable flashcards to help students engage active recall and confidence-based repetition
- A quiz with accompanying answer key to test knowledge and understanding of the module
A-Level Procedural and Object-oriented Languages (16-18 years)
- An editable PowerPoint lesson presentation
- Editable revision handouts
- A glossary which covers the key terminologies of the module
- Topic mindmaps for visualising the key concepts
- Printable flashcards to help students engage active recall and confidence-based repetition
- A quiz with accompanying answer key to test knowledge and understanding of the module
Candidates should be able to:
understand and use sequence in an algorithm
understand and use selection in an algorithm (IF and CASE statements)
understand and use iteration in an algorithm (FOR, WHILE and REPEAT loops).
What is sequence in an algorithm?
Sequence is a control structure where the computer executes the instructions in the order they are written. Each instruction cannot be executed until the previous instruction is completed.
Example: This pseudocode algorithm uses the sequential instructions INPUT and OUTPUT and will simply execute the instructions in sequence, starting at the top.
INPUT item_price INPUT vat_rate vat_amount = item_price * vat_rate final_price = item_price + vat_amount OUTPUT final_price END
How are selection and iteration used in an algorithm?
Selection and iteration are examples of instructions that do not have to be executed in sequence and are used to control the order that instructions are executed in.
Selection operations
These allow the program to execute instructions based on the outcome of a selection.
- IF – only if the conditions of the IF statement are TRUE then the instructions following the statement be executed and any furhter ELSEIF or ELSE conditions are ignored.
- ELSEIF (optional) – if the conditions of the IF statement are not true then a series of further checks can be made using ELSEIF. If any of the ELSEIF statements are TRUE then the instructions following the ELSEIF statement are executed and any further ELSEIF or ELSE conditions are ignored.
- ELSE (optional) – if non of the IF or ELSEIF conditions are TRUE then the outcome is FALSE and the instructions following the ELSE statement will be executed. If an ELSE is not used then the IF instructions are just bypassed and there are no alternative instructions.
- ENDIF – this terminates the IF/ELSEIF/ELSE selection.
- CASE – This is used with CASE OF and ENDCASE to select one instruction from a set of instructions, depending on the value of a variable.
Conditional example 1 – This algorithm uses the conditional control operations IF / THEN / ELSE / ENDIF.
INPUT hoursWorked IF hoursWorked >= 35 THEN payRate = 2 ELSEIF hours_worked >= 25 THEN payRate = 1.5 ELSE payRate = 1 ENDIF gross_pay = hoursWorked * payRate OUTPUT grossPay END
Conditional example 2 – This algorithm uses the conditional control operations CASE OF / CASE / ENDCASE.
INPUT hours_worked CASE OF hours_worked CASE >= 35 : pay_rate = 2 CASE >= 25 : pay_rate = 1.5 CASE : pay_rate = 1 ENDCASE gross_pay = hoursWorked * payRate OUTPUT grossPay END
Iterative operations
These repeat a set of instructions in a continuous loop until a set condition is met.
- WHILE – this is used with ENDWHILE to repeat a set of instructions until a condition is TRUE. The check is carried out at the start of each loop therefore the instructions in the loop may never be carried out if the condition is FALSE at the beginning.
REPEAT – this is used with UNTIL to repeat a set of instructions until a condition is FALSE. The check is carried out at the end of each loop therefore the instructions in the loop will be be carried out at least once.
FOR – this uses a counter and is used with TO and NEXT to repeat a set of instructions a fixed number of times.
Iterative example 1 – This algorithm uses the iterative control operation WHILE / ENDWHILE to carry out a block of sequential instructions until a condition is met. The check is carried out at the start of each cycle.
GET total_items SET total_cost = 0 SET count = 0 WHILE count < total_items GET item_price total_cost = total_cost + item_price count = count + 1 ENDWHILE average_price = total_cost / total_items DISPLAY average END
Iterative example 2 – This algorithm uses the iterative control operation REPEAT / UNTIL to carry out a block of sequential instructions until a condition is met. The check is carried out at the end of each cycle.
GET total_items SET total_cost = 0 SET count = 0 REPEAT GET item_price total_cost = total_cost + item_price count = count + 1 UNTIL count = total_items average_price = total_cost / total_items DISPLAY average END
Iterative example 3 – This algorithm uses the iterative control operation FOR / TO / ENDFOR to carry out a block of sequential instructions a set number of times.
GET total_items SET total_cost = 0 FOR count = 1 TO total_items GET item_price total_cost = total_cost + item_price ENDFOR average_price = total_cost / total_items DISPLAY average END